Well I would hope so. Do you know ONE insurance company that insures against PAST activities?
The gubmint.
However, with AA's recent history, apparently all the insurance companies which underwrite this sort of policy felt that the risk was great that more large-scale liability situations would come to light down the road -- not to mention that the liability for the Enron and Global Crossing situations isn't even close to being quantifiable yet. If any were willing to seriously discuss underwriting a policy at all, it was in a price range which would have exceeded what any potential acquirer was willing to pay for AA, thus rendering the policy useless for its intended purpose.
Not unusual. Doctors routinely buy "tail coverage" when they leave a practice. This
covers them against future malpractice suits. Tail coverage is, or can be, separate from
regular malpractice coverage.