It’s an additional […] point for water ingress.

the whole back panel is a big point of water ingress when that is not glued shut hard

It takes up space which could be utilised otherwise, like with a slightly larger battery or larger speakers or camera modules.

I never needed the additional camera modules, and there were phones with single camera module that made very nice images. the jack is also often at the top of the device where the battery doesn’t reach, but in my phone there’s also enough place for it between the bottom and the battery for a jack connector. in a fairphone

It’s an additional part which needs to be manufactured, stocked, installed and purchased. Extra cost which only benefits a few.

exact same opinion about multiple camera modules. nobody really needs them.