Very understandable to me. While the monorails weren't built with the park, they probably designed the space with the intention of putting the monorail in. They didn't plan the expansions that came decades later. So much of the cost would be tearing apart existing infrastructure to make way for a monorail. And really, the monorail is no picnic. Buses are a fine option more or less. Truth be told, I'd take a bus from the back of the MK parking lost to the MK gate if it was offered, so I didn't have to walk to the tram stop, wait for the tram, take the tram, walk to the monorail, wait for the monorail, take the monorail, and walk in the gate. The monorail really only benefits people who live in the super expensive hotels next to MK that are actually on a stop.