I think that making battery replaceable by user will affect the phone design. I had a ton of first-wave Android devices back in the day. I don’t remember carrying an extra battery with me. Maybe someone did, but how many of total users?

Another point is that making a phone water-resistant is likely not trivial when you can take the whole back panel away.

My point is: are these dramatic changes worth it when the battery degrades only couple years after purchase?