It leads to a lot of issues with the end design of everything. You either have to reconstruct the heap and all the pointers involved, or it has to be loaded at

It leads to a lot of issues with the end design of everything. You either have to reconstruct the heap and all the pointers involved, or it has to be loaded at a known address. With things like ASLR, and a bunch of other security features this ends up difficult or impossible to do directly anymore. Along with that, it also means that the runtimes aren't cross-compatible at load time so weird differences might leak out (little or big endianess, etc.). It leads to a lot of headaches because of changing systems underneath it.