> people won't want AWS/GCP/Azure to slap a UI on top of their free open-source product and resell it, making tens of millions of dollars per day in the process

Then build that UI yourself and sell it and make millions of dollars per day yourself, noone is stopping them.

Ah but you see there are 2 problems: 1/ "UIs" are harder than people think, especially by those that use that term derisively like you did. There are PLENTY of popular products that are basically just UI on existing data.

2/ AWS/GCP/Azure aren't slapping UIs. They're offering "managed operations" for these products. What is it? And sure, Hackernews is likely to scoff at that - we know how this site feels about dropbox -> https://news.ycombinator.com/item?id=9224

But if it didn't offer value, people wouldn't pay for it. Redis engineers are good at building a key value storage. AWS/GCP/Azure engineers are good at building managed operations. Combine them together and you've got the best of both worlds.

AWS/GCP/Azure aren't making money off Redis, they're making money off their experience in operating cloud infrastructure. And the free market wants to pay them to do so.