If you mandate everything has to have replaceable batteries, you restrict the ability for consumers to choose devices that prioritize other things.
Only logic that I would say could be used is an environmental concern, but you'd need to really show that replaceable batteries would lead to significant improvements in the amount of e-waste we generate. If everything has a replaceable battery, but only a few people take advantage of it and the average lifetime of a phone remains constant-ish, it's really not valuable.
I think the replaceable battery thing is very much a HN bubble issue. It's not like there aren't phones with them. If more people wanted them, more people would sell them, but most people prefer the additional battery life, increased water resistance, and thinness of modern phones.