Too many things. Cam Neely probably being the biggest personally but also grandpa's love of Bobby Orr, and my constant conversations as a youngun with him about how Lemieux, and Gretzky never really compared. Then you have Ray Bourque, Terry O'Reilly and all the other greats as well.
Then it's about the attitude surrounding the team. Hard work and pride being the key ingredients... and not righteous "we won 24 cups" pride either but a true pride in the history of the franchise and game.
I'd also have to give some credit to Montreal and Toronto as I absolutely loathe both and would continue to do so even if there were no team in Boston. Montreal is like the metrosexual at school, all about skill, flash and glam with a gigantic sense of self entitlement. Carrying that kids banner around rooting for their success doesn't appeal to me. Toronto is like the rich kid who passes his classes yet who you know is as dumb as a friggin post with that same sense of self entitlement. Again, not someone I'd want to root for.
Then the list continues... the more I wrote the more reasons I'd think of.