Until a few years ago, it was common for Android devices to stop receiving features after about 1 year and then stop receiving security updates after 2 years. Unless you're getting security updates another way, which may not work correctly and may even require you to build Android yourself, you should not use the device for anything important after that point. The batteries would be next to useless by that time. Now it seems more common to get three years, which isn't great either. iPhones last longer, but they come with all the iPhone problems.

The not easily replaceable battery shortened that time for a lot of users.

Yeah, some people get a new phone every year or so. I know a guy who trades in his "old" phone for a brand new model every few months. He doesn't really trade though,he just resells. It only costs him like 200 or 300 euro, if you factor in the resell. For him that's worth it, aparantly.

My last phone broke after about 1.5 years of me using it (and it was already a refurbished device), and my current relatively new-to-me phone only has 2 years of security updates left (also refurbished). I'm probably going to use it for longer than that if it doesn't break, but that would definitely be a good time to get a new phone if money was no object and I didn't give a shit about the environment.