It's either because they don't have enough stock, which is HIGHLY likely, or because the Google has publicly called Verizon out over Google Wallet. You think Google is perfectly fine with their FLAGSHIP development phone not having one of the products they're trying really hard to sell? Google isn't going to give up that easily. It's plausible that Google left it up to Verizon, or moreless assumed that Verizon wasn't going to go out of their way to disable Google Wallet.
It's not because of the LTE network. That's been established by Phil and just about every other blog/android news website on the internet since Friday. And at this point, it's not because Verizon wants to sell other products. Maybe that was why it was delayed in November, but it's certainly not the reason when Verizon already sent out stock to their stores. They WANT to sell this device. Period.
Oh, and it's not software issues, that should be painfully clear after people have bought the device already and it runs flawlessly. Including the 3G/4G network.
That said, not enough stock is quite possibly the reason for the delay. We should hope so, because that's pretty easily solved.