A more likely reason is that his stock options were probably no longer "in the money", meaning the strike price was above what the current trading price of the stock was.
As far as these loans from Enron, I think it will be revealed that these were actually a disguised form of compensation. I don't know for sure, but I imagine it worked this way:
You issue a "loan" to Lay, along with stock options sufficient to repay it. The stock options aren't taxed until they're exercised, and you don't pay tax on money you've borrowed. If the "loan" is used for investment purposes, you even get to deduct the interest from your income tax.
It's a sweet deal that most of us don't get from the company we work for.
But to all those who say that Ken Lay belongs in jail, I have just one question. For what crime?
It may not be as easy to pin anything on him as some here believe. It's not at all clear, for example, that the phony accounting was illegal. It's not going to be easy to prove that his stock sales were insider trading, especially if they were part of "program sales" in which he announced his irrevocable intention to sell shares in the future.
Don't misunderstand me. I'm not trying to defend this creep, and I think the political pressure will be strong enough that he gets indicted for something. But don't be shocked if it doesn't stick. He may be liable civilly for some damages, but criminal charges will be much more difficult to show unless we uncover some new damning evidence.