I agree there is a degree of proliferation but how many have you actually tried? They don't all work the same. There is a plurality of design considerations and options when constructing such an application. I stubbornly adhered to using metamask exclusively until honestly very recently and have had my eyes opened to the vast space of possibility when thinking about the human/web3 touchpoint interface. The difference in user experience between something like rabby or rainbow to metamask is vast, without even considering different chains or mobile. Trying more will give you an appreciation as to why the number of different available wallet apps is so high