DFW is a "joint" production of Dallas and Fort Worth. Both cities had to agree to close their airports so there would be sufficient traffic to make the fledgling regional airport viable in the beginning. Fort Worth closed Amon Carter field, and Dallas closed Love Field.
Without the agreement, there would have been no DFW.
And that would have been a bad thing?
No, they didn't close it. They TRIED to close it. They got all of the airlines to sign off on the deal before DFW got underway. Unfortunatley for AA, Continental and Braniff, Southwest began flying after the agreement, but before DFW was completed. No one thought to try to make them sign off on a move. (Delta also served the Dallas market, but at that point it was not a major player there).
When Dallas tried to close Love, Southwest sued and won. The airport remained, and remains, open. I believe that it is presently served by two airlines. At one point within the last 10 years, they were up to 5 airlines.