That's because many corporate "donations" are not so much a donation as a way of soft-buying a feature.
It's hard for businesses hyperfocused on short-term gains to understand a long-term value of, for example, supporting an alternative for an industry-dominating Adobe toolkit. But the value is there.
Long-term value that's hard to define doesn't translate well to stock price especially when any investment also helps competitors who aren't investing anything into the project.
Khara threw a bag of pachinko money in Blender's face to make the last Evangelion film work, and it was fine. I guess that was a rare occurrence that they desperately and so purely needed a tool they can hand to broke freelancers without frantically searching for keygens, but it can totally happen when incentives are right.
It's hard for businesses hyperfocused on short-term gains to understand a long-term value of, for example, supporting an alternative for an industry-dominating Adobe toolkit. But the value is there.