They like Brennan Scarlett who filled in when Simon was out for several games at the end of the season. And they probably want Clowney, Mercilus, and Watt on the field at the same time more often than not. I'm sure Simon wants to be a full-time guy.
Simon is way better than Scarlett. The money he got seems reasonable. I guess playing time could be an issue.
I wouldn't say way better. I didn't notice much of a drop off when Scarlett took over his role. Simon is certainly solid starter material though.