Yeah, that's why absolutely nobody bought color TVs back when those first became available.. /s

People care about things looking nice. In particular, people who pay others to create websites also obviously want their stuff to stand out, look nicer, and "pop" more than the competition - and the things the person you replied to listed is part of that.

And then they put on full page banners and autoplay videos? Bullshit

Todays pages do not "pop", they abuse.

That's not the fault of the underlying technology, if anything it will be EASIER for predatory adTech to display such things when the entire UI is rendered in an opaque <canvas>-equivalent. How do I get uBlock to block specific elements (like a video player) when there is no longer a discrete video element to block?

It isn't, but the sad state of affairs is that if it exist it will be abused.

... yes, and welcome to this thread which is about alternatives that tries to avoid that.