CR7s are high-CASM planes. Where do MAF/LBB/AMA/MFE travelers need to go such that hubs at DFW/IAH/HOU/DAL can't get them there?
There are some smaller regional destinations in the Mountain West, the Midwest, the Southeast, and the Northeast that are served by DL Connection but not by AA or UA such as ABR, ABY, APN, BJI, BGM, BRD, BQK, BTM, CDC, CSG, GTR, DHN, EKO, ESC, GFK, HIB, INL, IMT, LWS, PLN, PIH, RHI, CIU, TWF, and VLD.
AA and UA also sell connecting itineraries to domestic and international destinations without nonstop or 1-stop connecting service from MAF, LBB, AMA, MFE, and other destinations.
Three main reasons for DL adding service to MAF, LBB, AMA, and MFE include
(a) DL frequent fliers with Medallion status in DL hub or focus city markets who will avoid connecting on AA, UA, or WN whenever possible,
(b) access to smaller regional destinations not served by AA, UA, or WN,
(c) connections to and from international flights operated by DL or its codeshare partners.
AA and its codeshare partner BA can already get passengers to many European destinations from smaller Texas markets not served by DL such as MAF, LBB, AMA, CRP, and MFE with 1 or 2 connections.
AA/JL and UA/NH/CA can already get passengers to many East Asian destinations from smaller Texas markets not served by DL such as MAF, LBB, AMA, CRP, and MFE with 1 or 2 connections.
DL's partner AM already serves CJU, NLD, REX, MAM on the Mexican side of the Texas-Mexico border, and AM can also connect passengers to other destinations in Mexico, Central America, and South America from CJU, NLD, REX, and MAM through MEX.
AA also already serves many markets in Mexico, Central America, and South America nonstop from DFW, and UA and its codeshare partner TA also already serve many markets in Mexico, Central America, and South America nonstop from IAH.
WN also already has nonstop service out of HOU to a few destinations in Mexico and Central America.