You don't understand the whole context of the Avalon project. It is very simple:

Avalon was started by 2 young engineers who had almost no money (*), and no or little experience designing ASICs. They had no choice but to sell pre-orders at a low price (due to the overall risk and uncertainty of the project) to acquire the initial capital required to develop a 110nm chip and the machines ($200-300k or so). Once they successfully manufactured the first batch of Avalons, they honored the pre-orders because they are ethical persons. If they had say at this point "f*ck you, customers, we will mine with your hardware and not ship it to you", this would have enraged the community, destroyed their reputation (so no batch #2 and no batch #3 sales revenues for them), and it would have possibly disrupted confidence in Bitcoin due to 2 guys controlling the majority of the hashing power, possibly destroying the exchange rate and their potential mining profits.

That's why. If you knew the 2 guys, you would see they care deeply about the future of Bitcoin and about ethics.

(*) ngzhang did not make that much profits from previous FPGA sales, and yifu did not bring capital AFAICS.