According to Wikipedia - I know, it's not the most reliable of sources, but it's all I've got to work with - Gran Turismo 2000 was a working demo shown at E3 in 2000 and 2001, but delays in the game's release meant that it became Gran Turismo 3: A-Spec. Which is consistent with what I know about the game from a back issue of Official Australian PlayStation Magazine, which presented GT2000 as Kazunori Yamauchi's vision of a GT game for video game arcades.
So it's not that Gran Turismo 2000 was unpopular, but that it was never released.