I think there is a lot of confusion in this thread about whose responsibility is whose. The TSA is correct in that by policy they are required to be agnostic towards the status of anyone presenting themselves to the ID checker. Their jurisdiction officially starts at that point, not at the entrance to the queue. The airline rental agreements with the airport include the security queue spaces, and ultimately it is up to the airlines themselves to police premium line entrances, should they decide to offer them. At other airports such as EWR, you'll notice that it is airline or rent-a-guard employees (paid by the airlines) who enforce entrance to the premium line, not badged TSA employees. I'd kindly suggest to the OP that you were barking up the wrong tree with complaining to the TSA, as the real fault lies with WN.

At PIT, US Airways used to pay someone to enforce the line when they were the dominant carrier, but now it seems to be a free for all since no airline will step up and do it. Considering there are at least 6 carriers flying out of PIT including WN who offer a premium line benefit to elites, you'd think it wouldn't cost that much to split the cost of a minimum wage hire to check BPs, but I'm sure it's just a bureaucratic mess with no one interested in championing the issue.