Pywikibot normally uses two accounts: a bot account and a sysop account, the latter only for actions which need elevated permissions. When using OAuth as the authentication method, this possibility is not supported.
(IMO separate bot accounts are a relic of the past: OAuth allows you to prevent access to scary permissions like editinterface, and can tag actions that happen through OAuth, so there is no need for a separate account anymore. Workflows have their momentum, though, so it would be nice if it was supported anyway.)