As the WDW Monorails are a self-contained system, they cannot be subject to Federal Railroad Administration rules. That is the reason that most subway-like, trolley, and monorail services in the US are not subject to these rules as they either do not share track with conventional rail services or do not operate at the same time. Two notable exceptions to this in my area are the PATH trains between New York and New Jersey and the Staten Island Railway in New York due to their connections to the national rail system. The WDW boats are not subject to Coast Guard regulations for a similar reason, as the waterways that they operate on are not connected with the outside. When I started at the Friendship Boats, I was told that is why the flags on the WDW boats only have 48 stars, as only boats regulated by the US Coast Guard can display the regular US flag. Buses, obviously, cannot enjoy the same exemptions because they operate on roads that are linked up to the world outside of the purple gates.
As for doing more driving and less entertaining, the buses already have the Magic in Motion system in place that allows for that, though a lot of people seem to not like it for that very reason. (For what it's worth, while I enjoyed having chatty bus drivers, I am also quite a fan of MiM.) On the Friendship Boats, the spieling is now done by the deckhand, instead of the captain, for that very reason and also because it looks better when the person talking to you is actually facing you.