In one case, none -- extrepo carries a PPA for Trinity desktop: https://salsa.debian.org/extrepo-team/extrepo-data/-/blob/ma...

Generally, these are repos maintained by the upstreams themselves, e.g. Docker, Tor, Armbian, Dovecot... my guess (and it's just a guess, I haven't used Ubuntu PPAs much lately) the PPAs are maintained by not-the-upstreams. Or perhaps some of the upstreams are maintaining both a PPA and their own hosted repo.