Github is a lot of things to many people. A "web host" and a way of publishing information about software is definitely one of the things it is.
Most software is not popular opensource with a carefully curated web footprint.
(What would suit me, I think, is a view that was very much like the current one, but with the files list collapsed (but expandable). So there'd still be all the the tab-like row across the top, and the About column with releases link, and the main area gewgaws like branch dropdown and some indication of the most recent commit. But just with the README front and centre by default.)
But it's mostly just a sign of how almost nobody actually cares about the code now, and just use GitHub as a source of free libraries that may as well not have source available at all.
For others of us, a README is something we may briefly read once or twice when first considering or integrating a project, but the repo's code is where we spend way more time -- evaluating quality, tracing potential bugs, unearhing quirks and overcoming sparse documentation, considering whether a fork is needed, etc
But that's all hokey old greybeard stuff these days.