It's anyone's guess why the grey market for Star Citizen is so active, but from a very early point in the original crowdfunding run, it was clear that people were enamored with the ships. AD's theories make sense; there are a lot of people on SC's forums that forget or don't quite appreciate that shopping for and customizing your ship is supposed to be as big a part of the game as it was in Privateer or Freelancer (even though many of those upgrade paths were pretty linear). Lots of people seem to look at the ship hulls as sold in the pledge store as though they and their stock equipment are dispositive regarding what the ships can and can't do. For example, plenty of people obsess over whether a given ship comes with a jump drive stock or not.
That's not something anyone who's played Privateer would consider a big deal. I don't imagine that a basic jump drive would be difficult to buy at all. Despite the devs' repeated reminders that SC's meant to be a skill-based game, the notion of pay-2-win has become so firmly entrenched in the minds of a lot of people that they have endlessly cyclic discussions about whether this ship has any chance whatsoever against that ship or vice versa. Contrast that with most of us hanging out here, who might readily concede that a Scimitar is at a disadvantage against a Gratha, but wouldn't consider the result of a duel between the two a foregone conclusion.
Whatever the cause might be, the player/community focus on ships and any information related thereto in SC is extremely strong, much moreso than it appears to be for, say, Elite: Dangerous. But with the amount of lore and detail surrounding the ships, even in their very preliminary states, as digital goods go, a Star Citizen ship looks to be a pretty substantive pile of pixels to spend your money on, at least compared to a lot of other digital content. You could sit around and daydream all day about what each ship class might represent, and that seems to fuel a lot of the market lust.
I mean, I could sit here, right now, and ramble on and on about the possible differences between the Aurora and the 300i, as I'm not sure that the 300i simply represents an all-around step up from the Aurora. RSI's ships are said (in lore) to be built tougher and more rugged than those produced by Origin Jumpworks, so the Aurora might actually be able to take as much punishment or more once the shields are down. The 300i has more internal room that might be good for taking on passengers; there's pretty much nowhere to keep passengers on an Aurora unless they're willing to take the ride stuffed into the cargo pod. (The design intent for cargo in SC is for the actual containers to show up in your hold and affect the mass and handling of your ship, unlike Privateer where loaded cargo is just lines of data in your savegame file). And so on and so forth.
While the frenzy over owning your own ship in Star Citizen has done a lot to drive the crowdfunding numbers, my guess is that the grey market stuff in particular also ends up creating a lot of work for the Customer Service department. There are a variety of potential good reasons that Customer Service wouldn't favor babysitting grey market deals gone bad, but whatever they might be, the official policy is that grey market activity and promotion is not welcome on the company site, chatrooms, or forums.