Ethan Einhorn said that the time to get those games to work properly would have caused them to not have time to add the bonus games.
They still could have just forgotten, since that really does seem like a bullshit answer, but they did put that out there before the game released.
Personally, I think the collection was a good deal. Allowed me to keep my shit packed and still enjoy those games, annd they came out to like $1 each, much less than Wii's VC. The emulation isn't perfect, but we have had worse ports.