I think it has something to do with Walt's reputation. Not his public reputation, but his reputation in the game. He's Heisenberg, the man who makes the most potent meth ever cooked by man, beast or Seraphim. Jesse and Gail are the only ones who have come close, at 96 percent to Walt's 99 percent.
Now, even though Walter's "retired", he still sees himself as Heisenberg, the man who created this multi-million dollar meth empire. He needs this in order to make up for his selling his stock in Gray Matter right before it took off. Since Jesse is the only living man who can cook as well as him, he's the only one that can make him expendable and destroy his raison d'etre. Since the Czechs are dealing with shytty product right now, 96 percent should be good enough for them. At least good enough that it's not worth quibbling over the small gain in purity that they'd get from having Walt cook for them.
So maybe Jesse's gonna go to Lydia with some deal, words gets back out to Walter, Walter gets mad and comes out of retirement and Hank has a solid case.
Or maybe I'm talking shyt. I dunno.