People obsessed with the possibility that the preorder that's available might put them ahead of the diff curve and be first with the hardware to stay ahead, combined with lots of newcomers who don't understand diff rises and its effect on profits losses from mining. Usually cognitive bias is how people explain their losses away and they move on and possibly even do it again (wiki: post purchase rationalization). It's a market that seems to have no bottom to it, and we'll keep seeing it for some time to come.
The whole question is similar to asking in 1998 why people use AOL. The service was terrible, there were far better alternatives and no advantages beyond name recognition. Anyone who used them quickly learned they sucked and moved on to better options. They survived on massive waves of newbies, so many that they had no need to retain customers. Mining hardware has been exactly the same.
I personally think the MtGox press will shut down the flow of clueless newbs thinking they can get rich quick and choke off the pre-order money.
If it happens, some companies are going to go bankrupt, because they rely on pre-order cash for operating capital. This makes it doubly important to stop paying 100% upfront for gear because the next wave of pre-orders aren't going to be late, they will never come at all.
EDIT: On top of it all, I would be extra cautious about the solvency of the hardware sellers right now because some of them may have lost a fortune in the collapse of MtGox. 750000 BTC is a lot of deep pocketed people feeling very stupid right now.
& growing by the day 
