I'm guessing this only pertains to the handful of First Party and a few other premium games and not the acres of rubbish, which is actually half of the answer right there.

But Nintendo is also historically stingy in this way, they don't lower prices after few months like other licensors. Xbox/PS3 hits drop price after a few months or so. In part, they HAVE to, because there are always 20 other great games that just came out competing for attention. The Wii gets maybe 5-10 a year so they really milk 'em. It took years for the older Wii hits to finally get a greatest hits line ("Nintendo Selects").

I've noticed that lately Microsoft has actually more or less stopped doing their Platinum Hits line. Not much point anymore because there are so many great games, and they drop price on their own without need for a value line.