Well bare in mind that Final Fantasy I-VI (excluding III) were ported to the PSone, but were still left unplayed by a great many of those who were introduced to the series with VII. The thing is, following VII, the Final Fantasy became something of an entirely new entity, judged by completely different standards. The earlier titles (I predict) didn't match the expectations of new fans who had come to associate the series with huge sweeping drama, convoluted plots, and (let's be honest) 3D graphics.
As much as I love VII, I hate the fact that it so drastically changed the nature and standards of the franchise. It started us on the slippery slope that has now led us to Final Fantasy XIII