Very well put. I already found disgusting what AWS did with Dynamodb (adding key-eviction, etc as a catch-up with MDB) but this is even more hideous.
MongoDB has a terrible reputation when it comes to scalability and support. If you search you can find a bunch of horror stories. I don't have any angle to condemn or support this move, but it definitely seems like a response to what AWS customers and the market were asking for: "Give us a managed MongoDB or MongoDB-like service that doesn't suck"
Also it's clear that you have zero knowledge about Mongodb hosted services. Because otherwise you would know that very good supported hosted services exist which are 100% compatible with AWS (beside MDB Atlas).