I think, the difference is that AWS already has a bunch of core services that scale and uses them as a base for new services. (MongoDB->DocumentDB) Also, they

I think, the difference is that AWS already has a bunch of core services that scale and uses them as a base for new services. (MongoDB->DocumentDB) Also, they hear about the problems some customers have with an existing product and try to (re)invent a better solution. (MySQL->Aurora)