alt Hacker NewsYou are basically saying that you, from the outside, have solved the problem perfectly and the whole team of engineers at GitHub just don't know about this one simple solution you are proposing.
Have you considered that you don't have the full context of the problem and it's not "just" a few small tweaks?
My guess is that the problem is internal politics and incentives. Yes I think it is a fully solved problem for a company worth trillions to have an infinitely scalable "pull requests" page.
For example, Microsoft is known to pay significantly less than their competitors. I am guessing they just don't have the systems internally to say "This problem is worth literally billions to us in revenue per year, so we will pay millions to IC's to get it fixed and clear internal roadblocks".
It's not "just" small tweaks it is likely that people who are entrenched need to be moved and they need people with the right incentives in place to get it done.