If dirmngr starts in tor autodetection mode (no use-tor, no no-use-tor) and the local tor daemon is running, then dirmngr enters a "hard" tor mode that fails when tor goes away, with (for example):
0 dkg@alice:~$ gpg --recv $PGPID gpg: WARNING: Tor is not running gpg: keyserver receive failed: Connection refused 2 dkg@alice:~$
This doesn't make much sense from the user's perspective. They never demanded Tor, and were happy to use it opportunistically, but the fact that it was running when dirmngr started now means that they've lost functionality.
Normal users will respond to this by putting no-use-tor in ~/.gnupg/dirmngr.conf because "it fixes the problem" (see for example https://bugs.debian.org/927336). This actually decreases the use of Tor by comparison to a default autodetection mode that will fallback to non-Tor if the tor daemon is unavailable.
Ideally, the default autodetection mode would look for the tor daemon on every access to the outside world, so that if the tor daemon starts up after dirmngr, dirmngr would silently cut over to using it when possible, too.
Users who want to enforce the use of tor can always explicitly put use-tor in dirmngr.conf.