Because of Dungeon Defenders, a rather memory intensive game. Basically, the MegaMemory settings clears stuff in memory too soon, making the game crash.
There are different 'compartments' in Android memory management. Each program, when it gets loaded into memory, is assigned to one (or many) of the compartments. The compartments are given a priority that determines how important the stuff in them is. Stuff that you can't run without, like the kernel and core android services are loaded into the first compartment... stuff that you only need temporarily is loaded into the last compartment. When there is no more memory, Android goes through the compartments, starting with the last one, and starts clearing memory.
The SuperCharger script is adjusting how big each compartment is... so by default, the compartments are really small. Android sets aside a (relatively) small amount of memory for the core stuff and leaves a big chunk for everything else. The problem is that the 'everything else' isn't being managed very well and it eventually crashes. Also, some of the compartments are too small, so when we load a lot of programs that all need a part of those compartments, they fill up quickly, then start fighting with each other for the limited space. With SuperCharger, you're giving each compartment more room so those 'fights' don't happen as often.
So, if that all made sense, it should help you understand why the MegaMemory settings are good for multitasking, but not so good for one big program that wants to use all your memory at once.
