The marketing space is filled with all kinds of "plug and play" SaaS providers which offer detailed customer journey data and sometimes it's just straight up easier to add an "accept all" consent banner than to try and allow for hot loading specific 3rd party libraries based on customized consent options.
Is it the right thing to do? In my opinion, no. But I can also understand a situation where decisions were made on marketing tech before understanding the technical privacy implications. And then the implementation is handled by a team (potentially much smaller) that does not work on the actual product.