First of all, we are aware that the performance could be better. We are planning to improve it in the future, but currently there is no timeframe for this.
There are multiple technical reasons, but the most important one is that the framework we are currently using is not optimized for this kind of task. So it is a technical limitation of the technology we are currently using to draw the material library.
One possible improvement would be switching from displaying the material library on the GPU instead of CPU, and we could do the same with other parts of the Corona's UI.