1. Competing card companies offer much better cards than they used to, and include benefits that only Amex used to provide. For example, Visa Signature and Mastercard's competing product offer return coverage, extended warranties, free rental car insurance, etc.
2. One of the main draws of accepting Amex was that Amex's customer base was more affluent than that of other card companies, but that is no longer the case, partly because of #1.
3. Amex lost the Costco deal. That's a loss of a great deal of credit card fees, and 10% of Amex cards were the Costco card.
The court case was also seen as a blow, but maybe not if it got reversed on appeal. In any case, there are plenty of other problems for Amex to worry about.