I am not surprised. Simmons career reminds me a lot of Howard Stern's. Both Stern and Simmons changed the industries that they worked in. They are both ground breakers, although Simmon is still mid-career vs Stern, who has been around much longer.
For many many different reasons, Stern constantly clashed with the companies who he worked for, the FCC, celebrities etc... Although Simmons is not nearly as controversial as Stern, he has clashed with ESPN, other ESPN writers, Zeke, Goodell etc...
This is a HUGE short-sited loss for ESPN. People like Stern & Simmons don't come along that often. Like him or not, he is a huge creative force behind many of ESPN's recent popular and award winning successes. Sure, ESPN gets to keep Grantland, 30 for 30, and most of the writers & contributors that Simmons began/brought-in, but they lose out on all of what may have been in the pipeline.
Simmons will land on his feet somewhere with the creative freedom that he is looking for. I expect that whatever he ends up doing will be unique and interesting.
Can't wait.
Mk