Because GT5 Prologue was a Demo and it sold just 4 million. The people which wanted GT 5 are still waiting. Like the people which wanted FF 13 are waiting until it gets released. The Content of the Prologue is anywhere near the Content of GT 5 and the people knew this because its not the first Prologue. The GT Fanbase is a special one. I know people which will buy a PS3 only for GT5. You cant compare the Prologue with the Full game its just a Demo.
Just wait for the release of GT and then you can judge the Situation. If Uncharted 2 can move some Units. And hat a full precedessor. GT 5 will move way more Units.
Just remember the Sales numbers of the last 2 GTs
GT 3 14,89 Mio
GT 4 10 Mio
and the Prologues were always between 3-4 Mio
Every GT fan waits eagerly since 5 years for GT5 and if the expectations can be matched (and it seems they will) the Game will move a lot of PS3s. Its the first real next gen GT and the people are waiting for it. look at MGS 3 and MGS 4 even with a much lower userbase MGS4 sold better then 3 because it was the first Iteration of MGS on PS3 the same goes for GT5. It will probably be even more succesful then GT 4 was. But I doubt it will match GT3 Numbers.








