The bird on the left and the bird on the right, these are two very different compositions. Aside from that, what I'm saying is that more megapixels equates to more ability to crop and adjust the composition without sacrificing maximum usable size in print. You may be one of those shooters who "doesn't crop," and so, yeah, the difference in mp is negligible to you (and without cropping and recomposing taken into account, sure, it's not that many pixels). However, in my experience as a freelance photographer, magazine editors crop the hell out of photos for all kinds of reasons when an issue goes to layout. Because of this, they want the highest resolution images they can get, and in 2020, 20mp looks a little skimpy.
Hey, maybe that's why it's 20 mp. It's the 1DX mk. III
2020 edition! Get it?!