Earlier quoted context omitted.
The fact that pretty much no phones have a replaceable battery says something. And it doesn't mean that all manufacturers are somehow colluding with each. The market is very competitive and pretty much every manufacturer decided the trade offs are not worth the benefit. If Samsung or Xiaomi or Google could sell you a better phone with a replaceable battery, they would. But everyone came to the conclusion that the tra…
I don't think the objective is to make it a "superior product" in the somewhat circular way you're defining it (i.e., the market equilibrium that we settled on). It's one of several measures to try to have people keep their phones for longer and cut e-waste.
If there is any incentive to make a product better is to make it more accessible to their first party customers.