ok,

they use a container for many reasons, disc access time, when there are many files there's a huge TOC and that can become problematic ... such big file allows for internal re-ordering of files in CD doing entirely without the structure provided by the system ... not sure if that's clear to you, they open a single file in the PSP = 1 file handle; then content inside is laid out for efficient loading, PSP reads in a linear fashion (I'm pretty you don't hear the UMD drive going crazy) -> remember those DC games badly ripped ? unordered files, they were taking an incredible time to load !