Whatever you think of those companies in a wider sense, it's totally inaccurate to suggest that Microsoft, Google or Amazon haven't given anything back to open source.
E.g., remember when Heartbleed hit, and the world learned that OpenSSL was maintained by one person getting only $2000/year for it? Fixing Heartbleed was estimated to cost half a billion dollars world-wide.
Agreed, but the point of sharing software is that it's not a zero sum game. The thing you create once is not diminished by me using it many times.
But specifically, those two are examples of companies who started off FOSS, then got exploited by AWS.
Every FS-focused person gives them sh!7, but leaves Amazon off the hook because they exploited under the FS rules, which is an inversion of who actually does harm in the world.
Reference: most software in the Apache Foundation and huge portion of the container ecosystem.