Basic misunderstanding of basic economics and the industry. With three legacy carriers left, there is zero incentive for DL to do much at IAH. Everyone, including DOJ, when DL/NW, UA/CO and now AA/US were approved.
Get used to fewer choices, radically higher prices and the notion that DL could care less if OP jumps ship to UA and even less if he jumps to WN (just can't seem to find the seat selection map on their website).