It'd take a lot to get developer adoption and buy in to a separate product that AWS builds themselves, so they adopted Redis. Easy money. It's easier to piggyback on something that won while making lots of money from it and say "well, I helped..." if things chanbge. Then, they chastise the creators as bad people once the gravy train stops.
AWS benefited from hosted redis before contributing. It wasn't adopted out of benevolence. They're still doing it with Memcached, for what its worth.