My last (and first) smart phone lasted me for 6.5 years. It received one OS update, and stopped receiving any other updates about three years in. I was never concerned. My current phone is about 3.5 years old, didn't receive the OS update in May, and I wonder how long it will receive security updates.
Anyway, it's the sort of stuff like this article talks about, that I never heard of in 2017, that makes me wonder if I'll get another three years out of this device. Maybe with Lineage.