But that's most likely 1% of the market. They can have their own phones. The rest of us just want water resistance for accidental contact with water and easily replaceable batteries.
The overwhelming majority of people will never even contemplate trying to replace their own battery no matter how easy it is (unless it’s literally 90s/2000s-style snap on).
So no, the average smartphone buyer does not swim with their phone. Manufacturers had other incentives to make changing the batteries harder and there was no pressure from customers to increase the IP rating. In fact all you hear is people ranting how much it sucks that batteries are so hard to change these days.
Phones being waterproof is a huge QOL improvement