Where DFW was built was in the boonies at the time. Everyone knew that given a choice of driving all the way to DFW or to Love Field or to (I forget the name of Ft. Worth's airport--Meacham?) they would pick the shorter route; so, all airlines at the time had to agree to move to the new airport when it opened.
Not getting into the Wright politics (although I am for its repeal), just correcting a slight factual error: Meacham Field, which still exists, was replaced as Ft. Worth's commercial airport in the early 1950s by Amon Carter Field, later renamed Greater Southwest International Airport. ACF/GSW was located just south of where DFW now sprawls, on the far eastern edge of Tarrant County (Fort Worth extended their city limits out to encompass it). The terminal, torn down in the late 1970s, was located just southeast of the present junction of the 183 and 360 freeways, just east of where FAA Road ends.
Until quite recently there was still a section of old ACF/GSW runway still extant just northeast of the 183/360 interchange (it was used for law enforcement vehicle training), but I beleive it has finally been removed.