I think the problem really is, atleast what I thought, was that the binary wasn't something I'd pay for. I could trivially compile it myself. Additionally the price was IIRC quite high for some hobbyists like myself. Plus putting advertisements in the header (or was that a separate event?)
If it had been a 10$/a license for the binary I would likely have done that but at the time it seemed cheaper to just switch to nginx.
Also keep in mind the different audience. There is server admins and developers. When I wear my server admin hat and license software, that is usually because there is no or not comparable free alternatives that I couldn't setup myself in a few hours of work. When I wear my developer hat I'm lazy and I will pay for software to save a few minutes of work if it's good enough.
Of course, I don't agree with the people who said it had become closed source, that is silly.
That was when Caddy lost all its reputation for me.
Doesn't seem as bad as you are portraying it... certainly not "lost all its reputation for [you]" bad?
Which isn't a problem for you and me, but is for the kind of person that was attracted to it because it's easier than nginx+certbot, as I said in my initial comment. I saw 2 major users of it: this kind of user, and people wanting a small simple thing to stick in their container-based setup for HTTPS/reverse proxy duties. The latter more or less automatically updated to container images that do the build instead of loading a binary and didn't have a problem with even having to consider paying. For the first it was a problem, especially since the cost wasn't really in the ballpark of "I'd happily pay that to host a small blog".
Hm, this reminds me of the Caddy, the HTTP server with Let's Encrypt integration. It's still open source, but a while ago they made the binaries paid (if you want it for free you need to compile it yourself). They got a lot hate for that; people were even accusing them of having become closed source.