Google has released roughly every meaningful patch it has made to the open source software it was built on[1].
As for funding, that's definitely not true by the numbers last i looked (and definitely was not true in the past).
Without concrete disagreements, this is just handwaving. So if you make some, i'm happy to argue with real data.
[1] The only cases i can think of that this isn't true is when the Googler who worked on it left before they got a chance to do that (and nobody has picked it up since)
Chrome or Android seem like good counterexamples, where the software that most people use (Chrome, or Android + Google Experience) is specifically kept in two separate buckets, open source and closed source, so that Google can strategically keep some parts open and some parts closed.
The original complaint was about taking other people's open source (mongodb) without contributing back. Not "failing to release stuff it made itself". That's a completely different thing.
Even there, what i said is still true: Google has released every meaningful patch to the open source software it used in making Chrome/Android.
Like any sane kernel team, google tries to minimize it's difference with upstream since it has huge maintenance cost.
Microsoft gets all the news because it's a drastic change from normal behaviour.
Amazon, Google, Oracle et all just keep steadily contributing stuff. A lot of the work is also deadly boring and not headline capturing stuff.
Few simple queries to show the work they're doing just on the kernel:
Amazon: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...
Google: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...
Microsoft: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...
Oracle: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...
Have you seen the degree of investment Microsoft has made lately in Open Source? It's an upside-down world where Microsoft if a bigger champion -- and funder -- of open source than a company like Google which was built on Open Source software.