You were just lucky, because YouTube uses A/B testing and does not roll out anti-adblock-measures to everyone simultaneously. This gives UBO some time to react.

I haven't seen any ads for years either.

I use uBlock Origin, plus I've configured my Firefox to open YouTube always in a dedicated container, that logs me out of any Google-related stuff as I never upvote or comment anyway. Browsing YouTube anonymously might have helped.