If I remember correctly, OnePlus dropped support of one of their phones in under 2 years? Can't remember which one.
Well, my dad's old S5 got updates up until last year, so 4 years, that's more than long enough for most of us. LG on the other hand didn't even give 2 years on the G5...
So it's a mixed bag, and a lot of people got annoyed at flagships dropping old phones when Android introduced the must support native encryption thing, which e.g. LineageOS bypassed as they don't need Google's approval. My budget LG K10 for example had I think two security updates in its life, and due to a host of other things besides only the lack of updates, I refuse to buy another LG product (inc. TV). But that's a company problem, and not an Android problem.