They committed to running less 3 man line, doing less of what the Texans are using him for. They want more versatile people out there. So while he would have been a good replacement for Raji, he still doesn't fit their new version of the line where the players are supposed to be dual threats.

Brining him back is an admission of defeat in that plan and they aren't ready to throw in the towel.

But Pickett alone is no solution as evidenced by the numbers above. Whether this D was a worthy experiment is very much up in the air. Twice its looked colossally worse.