The Nexus 6 has been revealed to be carried by VZW, but every single phone that is sold with a contract at a VZW store requires a sort of "check point" test before being considered a phone worthy of the character. That checkpoint test, looks at how the specs stack up in their service ecosystem. If you have ever seen a video of a benchmark test or review for any phone, it is like that, but only meeting the standards the company has set for devices it has allowed. The Nexus 6, being the first Lollipop OS device, is probably hurdling through multiple tests that VZW is putting it through so that customer satisfaction will be at the highest point it can be.
With that being said, many users that bought unlocked versions of the phone are already pleased with the performance of the device, so it is a question as to why they are dragging their feet. Today is Black Friday for 2014, and that is a large amount of sales that they could have made, but failed to do so. Now we can only hope Cyber Monday will yield something for this device and VZW. We know from the Nexus 6 site that every queue that has opened when a new shipment of devices has been produced has sold out almost instantly, so I doubt that VZW is questioning the ability for the Nexus 6 to be a lucrative endeavor.
NOW there could be a problem on Motorola and Google's end. They could have made a bid system between the US carriers and said "the first three to give this much will get the first month of devices" (kind of like an invite system with the One Plus One) and VZW just wasn't quick enough.
The other possibility is that app developers for VZW bloatware are hitting hiccups with Android 5.0 because their apps, regardless of the OS, function as they are from Android 1.0. I have an iPhone 5 and it is like taking a trip down memory lane because their buttons and loading bars from pre-iOS7.
I know this information because I read a LOT of articles on devices, and carriers and if I didn't have passions elsewhere, I would probably be a tech-journalist. I am at least a tech-head. I also say this because I am in the same boat as you are RespectableJoe, I too am waiting for VZW to offer a plan with this device because I am tired of my faulty iPhone 5 dying at 80% because a battery malfunction (and this phone is my replacement to a previously faulty iPhone 5).
I wish the best of luck to you and for all of our sake VZW will put this phone on contract before the Holiday Season is over. I know I would like to unwrap a Nexus 6 at some point in 2014.