If you donate, there's no guarantee that everyone else is donating. So you end up supporting the free riders (https://en.wikipedia.org/wiki/Free-rider_problem). Which is a disincentive to donate.
One of the factors that made FOSS much more promotable was a sticker-price for acquisition and / or support. The actual amount didn't matter, psychologically though it needed to show that it had 'worth'. Ifnitnwas free, the business was worried thatvit was just someone's weekend hack. If it cost $5 per user then it was great value.
Not once did anyone raise the free-rider problem when we paid for FOSS. Frankly businesses are so focused on getting stuff done internally that the fact that someone else might indirectly benefit is irrelevant.
Basically if you are strict about trying to eliminate all free riders, you're going to break society in a vain effort to maximize fairness in lieu of effectiveness. Society works because everyone assumes that even if some things are unfair, most will manage and the ups and downs will average out over time.
In the example given on the wiki page, people who swoop in and take the last minutes left on a parking meter that someone else paid for but didn't stay long enough to use are supposedly able to break the system. But I think that trying to lock the system down tight and completely prevent that behavior could feasibly be more damaging to the health of the system than simply tolerating it as an occasional but mostly harmless exploit.
There's a few studies which show that some piracy and other free usage might actually help an industry's profits. Key word is "some"--there is obviously a threshold past which would become very damaging. But nonetheless, if one can set aside their outrage over unfairness (which is very understandable for somebody who has poured their life and soul into working on an IP or paid a lot to license it legitimately) then one can probably stand to benefit even from the thieves and freeloaders if they manage it correctly. https://www.fool.com/investing/general/2014/06/13/does-onlin...