True but getting less true by the day:

https://github.com/MichaelMure/git-bug

https://www.fossil-scm.org/home/doc/trunk/www/index.wiki

I don't think it is - are those issue trackers being adopted? Fossil is cool (as is any other DVCS that's not Git) but it has basically zero users and fewer by the day (as is any other DVCS that's not Git).

I think you've changed the argument from a technical one to a marketshare one.

Obviously they're not as popular but I don't think it matters if the people who want to use it are able to use it. (The emulator devs, sqlite team).