It plays too well into some large companies "Embrace, extend, extinguish" strategies for dealing with open technologies. By being hospitable to people that obviously should not be contributing (eg, people who submit PRs through github) the talented contributors are allowing themselves to be open to a DDOS. There are many more bad programmers than good ones, and the dealing with the legions of unskilled programmers hired by "tech innovators" in their efforts to cut cost could grind kernel development to a halt. Then poof.