Canon is a business. It is absolutely about selling. All EF lenses work perfectly, even better on RF bodies than how they worked on EF bodies.
Yes, new technologies, larger mount, etc. have unlocked new possibilities. I am not 100% sure a 28-70 f/2 would have been impossible on EF. Sony made 1.2 primes when people were saying that the E mount was too narrow for that. In any case, Canon needed some halo lenses to convince people to buy RF glass instead of simply continuing using their EF lenses. And convinced me they have
I know EF works better then ever on R cameras, I re-discovered a couple of my lenses that I was on the verge of selling because they were not performing on DSLR

and yes, of course it's about business, but also opportunity; they couldn't keep EF around forever as a permanent solution, as the adapter in the middle is a pain in the axx, and of course just redoing EF repacked with an integrated adapter (something I read they did with a couple of RF supertelephoto) would have been lousy...also because, let's admit, EF's are good, but not perfect...the two 50 L have horrible sharpness up to f4 at least, the 85 1.2 L has slow AF and lousy corners, and the 85 1.4 L is good but not as good as the 85 Art which is pretty cheaper.
So it was business, yes, but was also the need to adapt new optical schemes to the new flange distance, and to re-do some L lenses that weren't up to the task, in fact both RF 50 L and 85 L are now amazing even wide open, while the EF's were easily beaten by the 50€ nifty fifty at all comparable apertures up to f4/f5.6
Surely the 28-70 f2 would have been technically possible with EF, but at what size, and at what price, considering that both of them for the RF lens are stellar...maybe with the longer flange distance, a comparable EF would have been an even bigger beast to manufacture, and very few would have bought it, or could have afforded it.