Long-winded post, but I’ll try to keep it concise for GD.
I know not all Christian denominations believe in Hell. But there is a significant chunk that holds to the view that 1) Hell is eternal torment (not annihilationism or purgatory,) and 2) everyone who dies unsaved will go there.
A lot of Protestants/Baptists etc. hold to this view. I grew up in denominations that held that view. Plenty of preachers preach this from the pulpit. A lot of Christian colleges (I attended two of them) have this written into their official statement of faith. So a substantial chunk of Christians in the world do ascribe to this view, at least verbally.
But the way Christians live does not at all suggest that they think Hell is real at all.
Picture the most absolute worst atrocity or torture you can imagine - ISIS immersing people in vats of nitric acid, the Mexican drug-cartel living-skull death, the people in Tokyo who roasted alive during the firebombing of Operation Meetinghouse in March 1945, the fate of the people on the upper floor of the World Trade Center on 9/11, etc. As horrific as such people’s suffering was, it was still only for a few minutes or hours.
Now, if one ascribes to the view that Hell is eternal torment (which has plenty of Biblical backing,) then this means a fate 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 longer and worse than any of the fates mentioned above. Actually, much worse, since eternity is infinitely longer than a vigintillion years. Even a number like Graham’s Number doesn’t even amount to a speck of sand compared to eternity. And we’re not talking about eternity sitting in a cafe sipping cocktails or something; this is burning. You couldn’t withstand fire for longer than even 1 second if you were to stick your finger in the flame of a candle.
In other words, if one is a Christian who believes eternal Hell exists, then the question of whether you are headed to heaven or hell should be, by far, THE biggest concern/question of your whole life til the moment you die. It should be all-consuming. The short 80 or 90 years of life you get on Earth would be but the briefest blink of an eye compared to eternity in heaven…or hell. And Heaven’s ramifications are just as important as Hell’s. It would be like as if I told you that you were a participant in a game show and what you do today - in the next 24 hours - determines whether you receive a billion-dollar jackpot tomorrow or get roasted alive in a furnace. You would be spending those 24 hours solely devoted to making sure you end up on the good side of the contest’s rules.
But almost no Christians behave that way. They are much more preoccupied with questions like, “Did I turn off the stove when I left the house,” or “will my insurance cover this procedure” or “am I going to be able to pay off the mortgage?” than they are with the eternal fate of their soul - despite the fact that the Bible hammers home the point that anyone could die at any time without warning (hit by drink driver, heart attack, struck by lightning, plane crash, whatever.) Indeed, whether they are Heaven-bound or Hell-bound seems to be something that occupies no more than 0.001% of their thoughts. And whether you’re saved or not is no thing to be sure of; Jesus Himself stated that many people would be in for a horrid surprise to find out they were not Heaven-bound as they had originally thought (“Lord, Lord, did we not perform miracles in Your name…”) Many Christians often shrug and say, “Well, I prayed a sinner’s prayer at age 12, so I know I’m saved.” Really? If a billion-dollar jackpot (or, conversely, whether one has remembered to bring their parachute when skydiving) were what was at stake, these people would NOT be shrugging nonchalantly, they’d be taking the matter very seriously. How can the eternal fate of one’s soul be a shrugging-of-the-shoulders matter?
And trying to get loved ones - or even random strangers - saved should be by far the most all-consuming priority of any Christian’s life. These Christians are people who would do everything they could within their power to intervene and assist if an uncle, aunt, cousin, etc. were facing some sort of imminent danger on Earth, yet many Christians have nothing but a shrug when seeing their unsaved relatives persist unsaved on what is, ostensibly, a path to Hell. One atheist had said that if he truly believed in Hell, he’d be willing to crawl ten miles on his knees on broken glass just to save one soul. To be sure, there are the hold-megaphone-at-street-corner preachers “Turn or burn!” folks, but they are a tiny minority within Christianity. Logically, every Christian should be spending nearly every waking hour doing nothing but trying to save souls. But the average Christian spends perhaps no more than half an hour per year in evangelism.
Lastly, there will be those who say, “Well, we don’t spread the Gospel by words, but rather, we spread the Gospel by our lives and actions, so people will see us as a shining light and want to be like us.” But again, most Christians are not living like that at all. They do not live a lifestyle that makes anyone want to convert and be like them.
TL;DR; Christians claim that Heaven and Hell are real but don’t live at all like it’s real.