I'm going to also take a guess that even if GB did skip PAX, a lot of the people they'd want to talk to wouldn't be skipping it, so the quality of the content wouldn't be the same as in previous years. Frankly, it was just super poor planning on either GDC or PAX's part. Personally, I suspect it was PAX.
Honestly, the whole scheduling of PAX East this year is terrible. It's way too early in the year (earliest it's ever been) and on the weekend of daylight savings. Given that they're one of the few shows that can occupy the entirety of the BCEC, and thus likely has some negotiation leverage, I'm really curious to know how they ended up picking this weekend.