> Plenty of people have great motives, few have the means to execute on them.
Sure. Not plenty, but still a lot of people have the means, and few of them choose to execute. Larse Ingebrigsten was a CTO of startup that got acquired and now maintains GNU Emacs. Bram Moolenaar has had consistent job since forever (not sure what % of paid time is dedicated to Vim maintenance). Richard Stallman quit and made his first money selling Emacs tapes. Some open source devs rely on consulting work. Some (Like Drew DeVault) have actual sustainable business model that are not donations (and still give away their services when it makes sense). I do not know of gorhill, but my first guess would be that he has a stable job that pays well enough and doesn't encroach on his private life and hobbies, which I believe uBO is one of.
Oh, and to add to it, it becomes incredibly easier if you find likeminded people to join in. Linus Torvalds is able to take weeks off because GKH is more than capable to handle the work in his absence. Andreas Kling has Linus Groh as co-maintainer to review PRs even considering ginormous scope of SerenityOS. As with everything, more capable minds share the load.
On top of that, uBlock Origin is still just an engine. A large bulk of work (as admitted on uBO README.md) is done in the lists like fanboy's. They are also largely contributor driven (and sometimes donations).