From the almighty Wikipedia:
Currently, Bill Simmons appears to be embroiled in a feud with management at ESPN.com. When asked by the editors of Deadspin.com why he had not written a new column in over 2 weeks, he replied "I still love writing my column and only re-signed last year because I really did believe that we had hashed out all the behind the scenes bullshit and come to some sort of agreement on creative lines, media criticism rules, the promotion of the column and everything else on ESPN.com. Within a few months, all of those things changed and certain promises were not kept. It's as simple as that."
Simmons never seemed to be a traditional ESPN lackey, so this kind of stuff doesn't surprise me.
His columns, books, and podcasts were always top notch in my book.