Travis Sawchik at FanGraphs suggests the Rays dumping of hitters this winter had to do with their inability to hit the fastball:

Last spring, I detailed how the Rays had, over the years, created a cult of the high fastball. Nor did their commitment to the pitch waver at all during the 2017 regular season. The club’s pitchers remained fully invested in throwing fastballs up last year — despite some of the negative side effects (notably, the home run) suffered by an arm like Jake Odorizzi, whom they have since dispatched to Minnesota.

Interestingly, at least to this author, the Rays now appear to be paying closer attention to fastball performance on the other side of the ball — that is, with regard to their hitters. If you are among that class of hitter who has difficulty with the fastball, the Rays seem increasingly less likely to employ you. Tampa Bay ranked 28th in performance against fastballs last season, according to linear weights. This offseason, however, they have shed some of their weakest fastballs hitters.

As pitcher throw harder and try to strike out more hitters, being able to connect with a fast ball becomes more important. I wonder if the Rays will bring this up when they face the grievance panel?

Update: Here is a very good article on the grievances.