If someone gave you tens of thousands of dollars of valuables would you say thank you? If people gave that to you regularly would you become too bothered to say thank you? especially when your acknowledgement could help the person giving you their wealth?
In communication circles, people differentiate between requests and demands. The key differentiator: Turning down a request does not lead to anything negative. In particular, the requestor is not displeased or upset. If he/she is, then it was likely a demand disguised as a request.
On the other hand, fulfilling a request can, and often will, lead to a positive. It's still a request.
If you're going to be upset about it, don't phrase it as a request. A big chunk of the population will be annoyed by it.
Soapbox aside, getting to your comment: If someone is giving me that money unsolicited, I may or may not give a thank you. Context is extremely relevant. I did not give a "Thank you" to the recent stimulus check, for example. And I've definitely had fights with people voluntarily giving me stuff over and over and complaining about my not saying "thank you" (or even worse, not reciprocating). I've had to forbid them from giving me gifts in the future. I'm not saying my attitude is the norm, but it is "one of the norms".
The book Influence covers this topic in a lot of detail, and this is commonly discussed in Negotiations books. The bottom line: Be wary of gifts, and either reject if you suspect reciprocation is desired (which could mean "Thank you"), or make the understanding explicit and keep the reciprocity in mind. Of course, this goes at odds with several cultures.
As much as we like to talk about "open source" culture, it doesn't exist. It gets argued to death every time it comes up, which is a good sign it doesn't exist. A big chunk of the SW world, if not the majority, do not feel a need to reciprocate - even with a thank you. (Most of that chunk are OK giving a "Thank you", and this is not a contradiction).
not sure why you've been down-voted but I thought that was well explained. I do rather strongly disagree with your example as being relevant, but I think you've made a lot of good, relevant points. Your example of stimulus being a gift is incorrect. We explicitly pay into social programs as a society with full expectation that those funds will be used to help us. Stimulus isn't a gift.
