I always felt games were marked in those categories for two main reasons:
1) They actually were very popular, and to increase sales late inthe game's life, they would just drop the price and label them as such
2) The game always sucked, and to help boost sales, they include a sh1tty game with all the other "greatest hits" hoping to convince people that they really are good.
Also, most of the really great games don't hit that designation until way late in life, and for good reason from the Industry stand-point. If they continue to sell really well late in life, why drop the price? I'm mostly thinking of PS2 "greatest hits," and how long it takes games like GTA, X-Men Legends, and I don't know..."Bass Fisherman" to hit the category. San Andreas is 2+ years old, still not there. Legends did it in less than a year, maybe...and games like Bass Fisher are sent straight to "Greatest Hits."