Since Arrow was adding another degree of motion, the sideways swinging of the trains, it was difficult to predict what forces would be experienced throughout the layout. Specifically, Arrow did not bank turns with the Bat, which created excessive force and created a jarring rider experience. There was excessive wear on the train hardware as BBH mentioned (especially the shock absorbers), as well as concern for stress on the track.
You can see this in a promo video that was made by Arrow, featuring their suspended roller coaster concept. If the scale model that is depicted in this video is taken as credence, Arrow could very well have also considered the possibility of utilizing inversions.
[youtube]http://www.youtube.com/watch?v=miERaeQZYZQ[/youtube]
Bat faced so much downtime that it was the reason the Racer famously turned around the red train, to act as a replacement thrill for park visitors wanting to ride Bat.
The Bat in many ways was a true prototype, that allowed Arrow to fine tune their design to lead to more successful suspended coasters down the line; such as Big Bad Wolf, Ninja, or Iron Dragon. By banking track turns and beefing up the train shock absorbers, Arrow was able to deal with the swinging dynamics of the ride and minimize maintenance concerns.