Why would you be running on concrete when you can go to a park or a nature center and be running on dirt trails?
I can’t run, my knees don’t like it so I walk every morning. I do around 4mph and usually walk for 40-50 minutes. I have a treadmill, it’s in the shed, hasn’t been used in years. I enjoy going on a different path each morning, looking at the scenery, gardens, nature, just observing. Doing that on a treadmill, nah thanks.
About that « enjoying the elements thing » : currently -32 here, with a windchill of -40 to -50. Machines indoor (treadmill, rowing machine ) may be boring, but they’re not life-threatening.
Time. Convenience.
Why are most of my walks with my dogs in my neighborhood instead of driving out every day, or several times a day, to the forest preserves?
My indoor options allow me to roll out of bed and get in a half hour or so before showering for work, rain, blizzard, or shine.
My outdoor option combines dog care needs with my exercise.
Time and convenience are important aspects of keeping up with a habit.
Most equipment overstates the accomplishment. Do 100+ flights on a stair master and then go climb 20. 
If using a treadmill, stair master, whatever, I suggest just calculating the time your HR is elevated.
No idea how many 10s of thousands of miles I ran before my knees called it quits, but I’m not sure I ever ran 100 yds on a treadmill. Gets cold here in Chicago, but not as cold as Canada. Not sure I ever ran below 0, but definitely ran in single (and triple) digits. Now I bike. Heading out this afternoon when it will be a balmy 30!
Treadmill is likely better on your knees/joints than much outdoor running. And if you like to do it while watching TV, that is a fine option. I - and apparently others - think doing it outdoors, where all you need is clothing and shoes, is far preferable. And I tend to be quite interested in nature, so it is a great way to experience your surroundings and how they change on a regular basis. But if that doesn’t appeal to you and if a treadmill is what gets your carcass moving, more power to ya!
I loved that I could run outdoors whenever I traveled. All I needed were shorts, shirt, socks and shoes, and I could start as soon as I stepped out of the hotel. Learned a lot about cities I travelled to that I would not have learned otherwise. But if that is not something you want to do, look for a hotel with a treadmill. (I personally find hotel workout rooms exceptionally dreary spaces.)
Running is not my first choice for cardio, but treadmills have all the worst features, it’s the most boring and the easiest to talk myself into slacking. YMMV.
This thread is relevant to me, because I’m thinking of getting a treadmill.
Yeah. I walked some during the pandemic, but I’ve pretty much stopped. I think i might find it easier to prop up a screen and walk while i watch a show.
What other indoor options are you thinking of? Personally, i have knee issues, and i know i can’t ride a stationary bicycle. But i can walk indefinitely without hurting my knees, so i expect i can do that on a treadmill, too.
I haven’t tried an elliptical, but I’m afraid it might be more like a bike than a path.
Not which would work for you. I’m a fan of my Concept 2 Rower. I also have a non- motorized elliptical.
Surprised that a stationary bike can’t be adjusted such that it doesn’t bother your knees but it does.
There are the cross country ski machines … heck even jumping rope.
Some like one more than another but running is not the only option.
It must be unusual. I’ve had two physical therapists and an orthopedic surgeon tell me to try the stationary bicycle again, and each time my knee blew up and i had trouble walking for a week or more.
If using a machine to use while watching TV, you (obviously) want one on the quieter side.
I have seen treadmills that go to 45 degree angles - a tough workout for anyone. Rowers are the most economical choice for a good home machine (the NordicTrack ones often are on sale in December in Canada under six hundred).
For many machines the home ones seem much less robust than the ones at a commercial gym though I am sure there are exceptions and if you pay more you can get the same thing. And you don’t always need it - I bought an exercise bicycle that was cheap, but is exactly as sturdy as it needs to be and not one bit more.