Amazon can wrap an open source project in an AWS front end and create a paid for cloud service off the back of community effort. Or, key contributors can decide they want to take the existing code and change the license their contributions are released under going forward.
If the original license allows both these things to happen, then both are a risk and no one is being fooled.
I would love nothing more than for a project I built or contributed to wound up as an AWS service.
Writing the code is just part of the value, running it is also very difficult. Especially as the use increases and expose new code paths and bugs and what not.
What they can't - without giving the middle finger to OSS - is satisfy greed.
If you want to satisfy greed, fine, but be like Oracle. Sell a commercial license upfront. Don't pretend to be OSS.
The greedy people behind businesses managing OSS are concerned, because they are not satisfied with making money. They want to be THE ONLY ONES making LUDICROUS profits on top of community contributions.