I've never replaced a smartphone out of search for novelty, lack of updates or repair difficulties. Rather each of them got progressively slower over time eventually reaching a point of being unusable. And I'm pretty sure I have high tolerance for slow UI - whenever I asked my wife to do something on my last one, she would think it's not working at all.
How much of that is intentional on the vendors' part is an open question, but I'm sure they aren't losing sleep over it.