I am willsALMANJ. The Pentadactyl devs never responded to repeated attempts to engage them on the continued distribution of the addon. I could have posted it to addons.mozilla.org, but it didn't feel right to package their work unchanged when they had an official account and could have done it themselves if they wanted to. I made the GitHub repo partly so that my own browsers would get the compatibility updates and partly to help out others who wanted to keep using Pentadactyl. I like keeping the working xpi available for those who want it but I don't think it is worth promoting Pentadactyl any more because it is only a matter of time before Firefox changes too much for it to keep working.

I think because pentadactyl devs don't have any time to spend on it anymore. We (the community) tried to engage them in conversation on Github and through email for months before mandatory signing started, and they never responded.

FWIW, I use willsALMANJ's releases with no problems, he was/is quite active on the pentadactyl issue tracker.

Beats me. The scripts that automate all the signing are in the repo though. Maybe you can replicate it yourself. I haven't tried that though.