I agree that it card sending seems kind of rare; I certainly don't mind when I receive them, though! I do hope that when I send them, I'm not bugging people, but also like other people have mentioned, it's not worth worrying about too much because your wall is only available on desktop so I think most people don't keep up with wall posts unless they're other creators.
Until I hit 75 subscribers and made a new card, I used to personally write out people's names on the cards, too! It was fun, but it made me majorly procrastinate in sending out my thank-yous. And also as things begin to pick up, it's just too much time spent writing out people's names, making sure you're sending the right ones to the right person, etc. It's time that could be spent working on the next episode of a comic.🤷
Most people seem to be happy to receive one of my cards, but I did notice one time a subscriber deleted the card I sent them, LOL. Which is fine, they can do whatever once they receive it, hopefully they just received the sentiment that I appreciate them.
Here an animated card I have for my other comic series, too!