It's a very quirky thing. I'm PCG, and have been for years. But I never got the offer and was jealous of those who did.
About 5-6 years ago I arranged a meeting with my Fido guy to ask him about a few unrelated things, and when we were done I said "Oh, by the way. I've heard from some friends that they can get a free TurboTax from Fidelity. Is that true?"
He did kind of a double-take, and said "Gee, I didn't know you used it. I'll get you on the list."
Next tax season I saw the offer for the first time, and every year since then. So just being PCG or the equivalent is obviously not enough; there is some secret meshing of gears in the back office that has to happen. Anyway, it certainly couldn't hurt to ask. Some people here have asked and gotten both yes and no answers, so bottom line is that nobody really knows what the criteria are.