It's not just Waco, it's Waco/Temple/Bryan. Temple/Belton/Killeen/Ft. Hood/Copperas Cove has as many people again as Waco and B/CS each. We're only about 1/3 of the market. Growing faster, sure, but still a minority.
Splitting the #87 market (which is up, it was 94 last I checked) wouldn't make financial sense. Looking at the numbers, It would roughly be about #130 for Waco/Temple and #157 for Bryan/College Station.
At least we have local channels now (even if they are little sisters to Waco/Temple channels), with fairly reliable transmitters & cable/satellite uplinks -- 10 years ago, this was definitely not the case.