That hasn't been my experience, somewhat the opposite since people who donate money sometimes turn weird and controlling (even over pretty small amounts).
One can send thanks along with "No response expected or required!" :)
My social media bubble is one that comparatively spends a lot of thought on maintainter/contributor appreciation, and I've literally never heard that complaint.
No open source maintainer is so busy that they don't have the time to respond to a ever so rare genuine thank you with a "Thanks, glad you appreciate it!".
I can kind of understand where they're coming from. I've had people create issues or leave comments on random commits for the sole purpose of expressing thanks, which can get annoying in a bigger project. Especially when there are a few hundred people watching the repository that now each receive multiple emails they aren't interested in. That said, I still do appreciate people taking the time to express thanks when opening an issue or when I have helped them with a problem.
Yes, there are obviously some ways to express gratitude that are preferable to others, but as long as the entitled/ungrateful/"you are _supposed_ to do things this way" comments outnumber the thankful ones, I won't start complaining about them.
I've written one small open source library, which I publicized a little bit back when I first released it. Like you said, I wrote it mostly to scratch my own itch, but it was really nice to see it get some use out in the wild, and I have gotten a few emails about it over the years. Personally, I really enjoy getting any kind of emails about it from people who are using it or who have questions. (To be fair, I've never gotten the murdery emails abou it)
Open-source developers occasionally express dislike of "thank you" messages. They may have written that software mainly to scratch their own itch, and dealing with messages that don't say anything but thanks takes precious time out of their day. Donating money, however, is usually more welcome.