Disregarding the question of if the CSP compete fairly with providers of open source SaaS, your math is broken:
AWS revenue is about $90.76B, though most of it isn't from Redis, I'd assume. But let's be generous, and assume 10% of that is. So about $10mm. For the recent version, Redis-the-company contributions to Redis-the-software were less than third of the code base, so let's say they get $4mm. That's very little revenue for a company that has a valuation of over $2B.
Revenue is irrelevant, profit is what matters. The vast majority of the cost of any redis service offered is going to be the cost of the underlying compute and disk resources used. In some cases the margins could be close to nonexistent after paying for the resources utilized and the people to manage it, and it's used as a table stakes service that needs to exist for people to want to use your platform.
The vast majority of these projects didn't seem to have a problem with large companies like Netflix using their software, even if it was put on a cloud server, as long as it was managed by Netflix. Now that the management portion is moved to the cloud provider, along with some amount of possible profit, it's a large problem? Was it not a large problem when the companies were using these projects directly? Was there not some assumption and hope these companies would use these projects by the people contributing to them?
You must mean something other than 10%, that would be $9 billion by your numbers. 0.1% would be about $9 million so would be closer to your envelope math.
OP suggested the CSP should give 0.1% of their revenue to open source software they make their revenue from. As Redis isn't the only SaaS AWS offers, I was gracious and allocated 10% of those 0.1% to it.
Got it. It would actually be less than that since the number you selected was for revenue, not profit which is what OP asked for. Looking at some prior years it looks like AWS profit is close to 1/4 their revenue, so $90 billion would leave them with (generously) $25 billion profit. 0.1% of that would be $25 million and 10% of that (your estimate of Redis's share) would be $2.5 million.
AWS revenue is about $90.76B, though most of it isn't from Redis, I'd assume. But let's be generous, and assume 10% of that is. So about $10mm. For the recent version, Redis-the-company contributions to Redis-the-software were less than third of the code base, so let's say they get $4mm. That's very little revenue for a company that has a valuation of over $2B.