^Like someone said, the Mr. Freeze clones opened years later, which gave Premier time to work on their LIM systems. Also, running two LIM coasters simultaneously, or even alternating, is a HUGE energy consumer. There's a reason why these electromagnetically-launched coasters have their own generators. From ultimaterollercoaster.com, about Wicked Twister at Cedar Point:
But LIMs come with some unique requirements and Cedar Point has to install a dedicated 34,000-volt power line that stretches four miles for one purpose: to power the coaster. With all this juice Wicked Twister's train will reach a speed of 72 mph in just 2.5 seconds. And that's wicked fast!
"We're using such a massive jolt of electricity to operate Wicked Twister that it would be enough to power 550 average-sized homes," said Monty Jasper, vice president of maintenance and construction at Cedar Point.
Now imagine launching two of them, for a while at the same exact time. You can see why the park couldn't handle them, right? And I'm sure the system's problems all stemmed from the power overuse.
And then on top of it you have the problem of the forces in the barrel rolls. I never got to ride them myself, or the ride at all - I only got to see it being taken down. But I have to imagine that hitting a roll like that, especially backwards when your body isn't expecting it, stresses both the body and the trains pretty hard.