But I'm in their target market and I don't want a replaceable battery. I just want the battery to be serviceable when it wear.

For a given phone size, a replaceable battery require some additional space which means it will be smaller than a non-replaceable one.

I don't want to buy one or two additional battery to carry with me when I can get a battery that last a bit longer and that I can charge with any power bank. (mine or the one of a friend as there is no compatibility problems)

Users who want replaceable battery are niche in the niche.