Is it nature, nurture, or a combination?
Many hot spices contain capsaicin, which triggers a sensation in the TRPV1 receptor. There’s certainly a genetic component to the degree of sensitivity of this receptor in a given individual. At the same time, a receptor can be desensitized from prolonged exposure to the stimulus that triggers it; in other words, if you often eat spicy, your tolerance for hot food will increase. That means that getting used to it from an early age helps: If your parents cook spicy, and from your childhood on you eat their spicy food, it’s more likely you’ll develop a liking for it that will last into adult life.
So in summary, I’d say it’s a combination of both.
I have a wide variety of sensory sensitivities, and spicy food is one of them. I experience hot seasoning as painful, not stimulating. I also find this true of carbonated liquids, mint toothpaste … so it’s not surprising. I like the idea of ‘sensation seekers’ enjoying spicy foods but my husband douses things with hot sauce labeled XXXX, and he is very far from a sensation seeker. For one anecdote.
My mouth/tastebuds/pain receptors are all open to spicy foods, which I love with a passion.
With age, my stomach and gut disagree with all of the above 
I’m sure that’s right. When I was growing up, we never had food that was the least bit spicy. Well, sometimes we would get pepperoni pizza, but that was the absolute maximum spiciness. So even today, I can’t tolerate more than a tinge of spiciness.
I am not a sensation seeker but I love spicy food. I especially like it since being on a low salt diet.
If you want to change that, you can gradually adjust your tastebuds even in adulthood: start with something that seems slightly hot to you, then try something a little hotter, and so on. My sister still can’t eat any spice with any heat to it at all; I now like some of it, though I still can’t eat really hot stuff. I could probably work up to hotter, but don’t know that I’m going to.
Spicy food tends to be healthier, and people tend to consume less of it. If one only has access to a small number of bland or mediocre foods, it can make them more palatable. The whole reason the spice trade took off is because food storage methods and freshness were not always optimal.
On the other hand, I have no idea where I got my love of spicy food. My mom is an adventurous eater, in that she’ll try almost anything once, but for anything spicier than mild salsa, it’ll only be once. And my dad literally believed that capsaicin was the tool of the devil. Meanwhile, when I go out for Indian, I’ve only found one place around here that makes it hot enough for me, and that only if I ask for a 12 on a scale of 1 to 10. At some point, I just started eating it, and I liked it, and I can’t even remember when or how that was.
I eat the spiciest food of my immediate family, but most of us like it to one degree or another. But as Dogginit mentioned, I’ve reduced the quantity and intensity of my prior levels because of internal distress as I’ve aged.
I find that an axis of sour/hot or sweet/hot bring out a lot of other flavors that would otherwise seem bland, especially when cooking with cheaper cuts of industrially raised meat which seem bound and determined to be grown for maximum blandness.
So, as an example, if I was making lamb, or (quality) beef, or duck, no, I don’t want or need a hot sauce. Battery raised chicken and pork? Hell yes I want a powerful sauce to go with - although a strong herb option is fine, but normally at more of a premium than a homemade hot sauce.
And of course, living much if not most of my life in the Southwest and NM, I fully associate most Southwestern USA Mexican foods with a solid dose of hot peppers (less than Thai food though).
Was born in NM, home is SW Louisiana, spent a lot of growing up years in both East and West Texas, which explains my sadness with my spicy limitations now. Whether Hatch green chiles, spicy Cajun and creole dishes, and real chili, it leaves me depressed 
I thought part of spicy food was it helped make you sweat which would cool you off. A welcome thing in hot climates where spicy food is popular.
Because it’s tasty.
^This.
I like it because it’s tasty.
No doubt if you grow up with it, that’s what you eat, but I didn’t. I grew up on a bland diet, the spiciest thing in the pantry was Worcestershire sauce.
I went to a Mexican restaurant in my early 20’s and nearly died at the heat of diced pickled jalapenos. I put myself in the category of Sensation seeker. I decided (for some reason) to start pushing the boundaries at how much heat I could take in food and still enjoy it and I got used to hot and spicy stuff and really enjoy it. Habanero Tobasco sauce is a go to on eggs and I reckon once you get used to it you get a dopamine hit from the hot stuff.
Because I grew up in a very “afraid of spicy foreign foods” family.
Our meals were boring. They were food, that was it. Cold sliced roast beef, a baked potato, and a side of canned peas were about it. You want to spice things up? There’s the salt and pepper. Those were our meals, pretty much every night that I was in elementary school. It kept us alive, I guess, but it was boring. Even into high school, it’s food, it’ll keep me alive. Big whoop.
You better bet that when I was allowed to discover Chinese Szechuan and Indian curries, during my undergrad, I took the chance. And I did. And they were delicious. Spices made the food more flavourful to this guy who had never had flavour in his food before.
I’ve never heard the term “sensation seeker” and I’m having a hard time differentiating that from someone who just likes variety in their diet and food in general.
I didn’t grow up with spicy food, but it wasn’t bland or strictly American either. We’d regularly get BBQ ribs, Italian (which in the 80s and 90s was still somewhat “foreign”), seafood, Mexican, Japanese, and especially Chinese. It wasn’t until college that I discovered the wonders of Thai and Indian food. I did blow my face off a couple of times, but I’ve never looked back. Add Cajun, Korean, and Vietnamese dishes to that repertoire, and most, but by no means all, food I eat is spicy in some form. Does that make me a sensation seeker? I don’t think so.
This review article (cited in the Wikipedia article on pungency, so OP may have seen it already) discusses studies on culture, exposure, gender, genetics, and personality as determinants:
And i am a sensation seeker, but i have a strong dislike of spicy food.
In general, birds aren’t sensitive to capsaicin - spicy, and mammals are, and i think many plants are spicy because they “want” their seeds spread by birds.
Wild Birds Unlimited - Nature Shop.
In general, if you can tie reaction X to chemical receptor Y, you will find that some people have more Y, or a more sensitive form of Y. So there’s going to be an element of nature. But i assume we all know people who have increased or decreased their tolerance for capsaicin over time, because they ate more it less of it. So there’s also an element of nurture.