I wrote a post about this! the problem is not that there is no money, or that they don't want to donate, it's that there isn't a good way for them to donate.
You’re on target with this. Companies can’t contribute to random OSS on GitHub. In order to receive donations from large corporations (money and/or commits), OSS must be affiliated with a nonprofit that is properly structured and has recognized governance practices in place.
My sense is that a large company prefer, and feel more comfortable, partnering with organizations like the Linux Foundation or Apache Software Foundation.
https://medium.com/@paulbiggar/how-to-fund-open-source-8790e...