That's because you're not simply a consumer but also, and most importantly, an investor.
Actually you're not an investor. An investor gets a return on their investment. You are simply a consumer, but the Trezor has large upfront bootstrapping costs.
Soliciting funds for preorders is a LOT less risky for the makers of the Trezor then doing it the "traditional" way, which is taking out a loan and and paying the upfront bootstrapping and manufacturing costs with it, and finding investors and giving them equity in the company in exchange for bootstrapping funds. It is, however, MORE risky for the consumer, because you just forked over $200+ and you're not gonna get anything for it in the near future. Especially when dealing with bitcoin payments, the Trezor team could easily just disappear entirely. I don't think that's probable - the guys behind it seem like good people with good intentions who want to make an honest buck. But this has happened in the BTC community before, where someone solicits a large amount of funds then disappears.
It's also possible that they could hit a snag halfway through manufacturing. Suppose they use two companies to produce the two parts of the product, then they combine the parts together to create the finished product. They order 10,000 of Part A and 10,000 of Part B, but the company that makes Part B only makes 100 units before it goes out of business. Now, the trezor guys have to find a new company to produce Part B. But Part B costs 3x as much at this new company, and they've already reinvested the profit they've made, so they can't afford the extra costs and go out of business. Once again, this is not a likely scenario, but just an example of the type of risk they're pushing onto the customer.
TL;DR; You have to preorder super long in advance so they can shift the risk onto you instead of having to bear the risk themselves.