But it is not the reason given why most jams do not allow it. They say so in their rules.
Also a lot of jams do allow ai to some extent. If there were ethical reasons to not allow ai, those jams would forbid all ai usage.
Oh, and the actual Olympics do allow that you be carried by an enslaved creature https://en.wikipedia.org/wiki/Equestrian_events_at_the_Summer_Olympics