I put that down to most of the characters people remember (and like) being from those first two years. While Hasbro picked the characters who were on the poll of who should be nominated, it was the fanbase that voted for them. Said fanbase picked what it felt were the ones who deserved Hall of Fame status, and those nominees were overwhelmingly from G1, regardless of what they did in that generation. What did Jazz do that distinguished him, aside from being the only black robot on Cybertron? He wasn't a leader, didn't have a particularly memorable personality (or voice), and to my memory didn't really do much anything special.
The same goes for Bumblebee. The problem I have with his automatic inclusion is that he effectivly vanished from the franchise from G2 until the movie (comics notwithstanding), and his recent popularity is the result of the movies.