I know what you’re thinking: how can Google do this if Android is so open? Well, it’s open to a point, and it’s always been that way. There are certain rules in place that Google simply can’t bend on, whether it be to protect user information and privacy, to protect developers, and to protect the Play Store from malintent. That said, these developers are free to distribute their apps elsewhere, but Google won’t allow that bidding to be done in the Google Play Store.
It makes sense for Google to stop something that is completely counter-productive to their business model, regardless of how “open” we wish Android to be.