The main two reasons are the system's complexity and the the 50GB disc capacity.
I myself have ripped a few
PSP games and those are only about 1.7GB.
Many
PSP ISOs are compressed into CSOs that can go down to about 700MB.
1GB max.
Think about how long it takes to pirate a
PSP game. (With all the leeching torrent bastard...)
Now think about the same thing...but you're trying to download 50GB.
It would be nuts.
However, I hear Dark_Alex is getting to work on the PS3 systems.
I hope for the best.
Though...I'm not really for piracy.
I hope more homebrew is enabled.
Maybe this time he'll forget the ISO loader.