AMR never intended to fill flights on these routes...only put a carrier out of business. They did that (through the flights as well as the same judicial system tactics they used against WN in the beginning to try to get them to run out of cash) and then pulled out of DAL. But according to the company's press at the time, it was a very wise biz decision to fly all FC out of DAL and there was a huge market. AMR was simply taking care of its customers per their press back then. Amazingly, though, those customers were no longer important after Legend was successfully plowed under. Talk about both sides of the mouth...
I'm getting old, too, but my memory of AA's DAL flights is a little more clear than yours; AA didn't cancel DAL service until almost six months after Legend folded, and might not have canceled DAL service if 19 worthless pieces of trash hadn't attacked us on September 11. We'll never know, as AA's DAL service ended that day. Along with about 20% of AA's capacity, some of which has returned.
If customers were clamoring for (and willing to PAY for) 56 seat all-F service from DAL, you can bet your last nickel that AA would be offering it right now. The fact is, DAL service with 56 seats probably isn't as profitable as Legend thought it would be, and that's probably why AA didn't restart DAL service in mid-September, 2001.
It might also explain why no other airline has offered 56 seat DAL service in the past 4+ years as well. If it made any sense at all, wouldn't UA or CO or DL or US or NW or AS or FL or F9 be trying it?