That was true 15-20 years ago. Nowadays changing the phone is basically because:
1) battery dying / not lasting enough
2) shattered glasses whose replacement costs 35-40% of the cost of the phone new (for budget/mid-range phones, not everybody has iPhones)
distant 3rd) not enough free internal storage
Unrelated note but, cheap/midrange phones are a scam, you almost always get better value purchasing a second hand premium one.
also camera just not being satisfying enough anymore is a big deal
sure on highest end phones you have very good cameras since a long time by now, but even there they find improvements here and there (e.g. zoom, low light pictures, even better image stabilization)
but middle to lower end phones are still have major improvements in every generation of a certain brand/line/price category. And you might be satisfied with a "acceptable" quality camera, until everyone around you has way nicer photos, or you now have a reason to make photes you didn't had in the past, or you get older and your hands a bit unsteady etc.
Batteries are generally a cheap fix from third party stores. If you wanted to keep the phone why not spend the small dollars and just replace the battery?
Because you need to bring it to a shop, sometimes they may keep it for more times, sometimes if they are not that honest they will find something else and factory reset it and a long etc. If it's something one can do at home by one self as an expected and supported by the vendor operation, why not? You can still bring it to a store if you don't feel like crafty enough to do it.