Well, Superman: Ultimate Escape is a LIM shuttle coaster, even though it is not built by Premier, and Superman: The Escape is also a magnetically launched shuttle coaster, again not built by Premier and also an LSM coaster.
The two Mr. Freeze coasters and Batman and Robin: The Chiller are the only Premier LIM shuttles(I think), and they were all built around the time of the movie Batman and Robin, of which the major villain was(big surprise): Mr. Freeze. At that time, Six Flags seemed to be REALLY intent on superhero rides(even moreso than today), so it is more of a timing thing.
So, to sum up....
The Premier technology was at a high point in its novelty at the same time that "Batman and Robin" came out, which was at the same time that Six Flags was looking to pour some $$$$ into coasters at some established parks.
*** This post was edited by SFAGuy on 11/25/2000. ***