I can't see companies turning on the very resources they are using to say they are PCI compliant.
The merchant doesn't care who they spend their money with - they just want someone to tell them they're compliant. They are not likely to turn around after being certified as compliant and rat out their certifiers.
They would then run the risk of having further costs to re-certify under different QSAs.

The council’s PCI-compliance program includes a feedback form that merchants are supposed to fill out that would let them divulge what transpired with a QSA, but Russo acknowledges these forms aren’t always making it to the council. The council is considering hiring a quality-assurance specialist to keep an eye on the QSAs. “We’re interviewing now for a quality-assurance person for this,” he says. One thing the specialist will be doing is talking to merchants to find out if they were coerced into buying products.