Part of the reason PS2 backwards comp. worked well is because of the success of Playstation. (yes, duh, BUT THERES MORE!)
The success equated to more product in consumer hands, which equates to more used copies and prolonged circulation of the older software.
Gamecube software availability is nowhere near that, so this is a way to allow the new users access to a library of games highly underrated because the gaming community was having a small-dick crisis at the time(and still is!). Of course, Nin will probably rip people off for it, considering used GC games are in the $10 range.