One of the reasons I like donating to local charities is that I get a letter from somebody saying thank you. It is small, but it warms my heart. Even at $10,000 donations, I have never got anything from a national charity other than more requests for donations.
Those thank-you notes matter, even if fundamentally the reason for giving is completely based on the actual work.
I assume this is why the parent poster said "I suppose this shouldn't disappoint me". People shouldn't need a thank you email, but it's apparently valuable enough to at least one person to make a difference for them. How people actually behave and react to things is what you should design around, not how people should ideally behave. Given this (admittedly extrapolating from one data point), and because the cost of configuring a bot to send thank you emails is so low, I'd probably set it up if I were accepting donations.
I think it's entirely unsurprising that people would like a thank you email. If you donate to an open source project, you have gone out of your way to acknowledge the project's maintainer. The least they can do is acknowledge you back - it's basic reciprocity.
>the cost of configuring a bot to send thank you emails is so low
Honestly, I think a bot saying "thank you" is as soulless as no "thank you" at all. It doesn't take long to type up a manual response and genuinely express your gratefulness.
I occasionally donate small amounts to individuals active in open source and had the same experience as earlier poster.
I'd be perfectly happy to get a bot reply saying thanks. The main issue I had with silence is when I'm not sure if the money actually got to the maintainer.
I'm less worried about getting personalised 'thank you' as it is easy to see if the developer is still making active contributions.
Those thank-you notes matter, even if fundamentally the reason for giving is completely based on the actual work.