For infrastructure tools that are typically adopted by an entire org or company though (as my products are), the situation is less understandable to me, even in the scenario where the user is a small bootstrapped company or solo dev.

I mean, my own company is small and bootstrapped, and I still pay for a number of commercial products because they provide benefit to my business or my own productivity. If I ever can't afford them in the future, that would probably indicate there are deeper existential problems with my business besides needing to rewrite some code to avoid use of those commercial products :)

Also, personally if I wanted to give money to open source software but was unsure about the future affordability of doing so, I would especially focus on donating to open source projects that are actively soliciting donations in the first place -- rather than arguing with a business owner over their lack of interest in donations, which is what some users have done in my case.