yes there are books and comics but like GL said, anything beyond the 6 episodes is "made up" meaning it doesn't happen. so if he were to make a sequel trilogy, all of those books and comics would go down the drain being meaningless to continue. that may be an added reason to him not doing the sequel trilogy. and fans rather see a star wars movie or show any day rather than read a book. but your point is fair, plus the star wars timeline seems to be going backwards than forwards. It would seem the further the franchise goes back in time, the better it gets.
We definitely do not need a Star Trek situation where, us fans, have wasted the last 35 years to have it all be erased.
IMO, if Lucas wants Star Wars to last, he needs to respect what he's allowed others to do, for the most part.
I mean, things like "The glove of Darth Vader" can be dis-guarded but when you have let people write entire histories-with approval of your company-to just throw it all away and tell your fans "screw you. I got your money, now I'll make all that you bought worthless to have read, listened to, watched and played."