I think it's because FF8 is different from other FFs, and it isn't as easy to understand. People who dislike it usually suck at it and/or don't understand how the Junction system works. So instead of blaming themselves for being complete idiots, they blame the game.

I love FF8, and I have spent more work on this one than any other FF that I have played. I have a hard time choosing whether I like 7, 8, or 9 the most. They are all magnificent games and should be played by anyone who is a fan of the series.