Darth Caedus
Formerly Congerking
And you guys are telling me there are other jedi and force users who survive past RotS, so why not get their help? Plus, Obi-Wan thinks Vader is dead, presumably, so with one sith out of the picture, the jedi don't try to do anything? It makes no sense--one of the dumbest strategic moves in the series, and that says alot.
I never really got that myself...but it IS Lucas writing, so that explains it
BUT, you have to remember that Palpatine WAS the chancellor and Obi-Wan and Yoda would have to fight through pretty much the entire planet of Coruscant to get to him (unless they sneaked in).