The reason - Jann Wenner, co-founder and publisher of Rolling Stone magazine, has way too much influence and say on who gets in and who doesn't. When classic R&R artists such as -

Steve Marriott, Chicago, Deep Purple, KISS, The Monkees, Electric Light Orchestra, Yes, Stevie Ray Vaughan, Motörhead, Jethro Tull, Linda Ronstadt, The Miracles, The Marvelettes, Mary Wells, The B-52s, Emerson, Lake & Palmer, Rush, The Guess Who, Bachman–Turner Overdrive, and The Moody Blues

are kept out while non R&R acts such as -

Madonna, Beastie Boys, and other artists of this nature

are allowed in, all based on the mercurial whims, likes, and dislikes of ONE MAN, that's when rock fans of good conscience have to stand up and say ENOUGH! This man must be removed ENTIRELY from the decision-making loop and he must be removed NOW!

The solution - We need to spread the word on this petition, sign it, and push until it gets acted upon! We need Mr. Wenner removed from the equation ASAP to be replaced by a qualified, INDEPENDENT PANEL, with NO connection whatsoever to Mr. Wenner, that will be charged with voting on inductees into the R&R HoF! We, the fans, are what drive rock and roll! It's OUR music and OUR Hall of Fame! Mr. Wenner needs an object lesson in the power of the people! 

(Source - http://en.wikipedia.org/wiki/Jann_Wenner)