My recollection is that he was one of the people axed by either John Hart or Mike Cramer during one of their periodic purges, and Nolan Ryan, it sounds like, was instrumental in bringing him back.
From Richard Durrett's blog post:
To the average fan, this move may not seem like much. But I can tell you Blake is a good baseball man and a good guy, so it's nice to have him back with the Rangers.
If I'm wrong about Blake being run off by Hart and/or Cramer, hopefully someone will let me know.