EWR-IAH is a hub-to-hub megafortress route on which CO has no competition.

LGA-IAH has competition from TZ's LGA-HOU flights, but apparently CO doesn't have quite as much desire to smash TZ as they do B6. Either that or TZ hasn't been pushing prices down as much as B6 (although I recently booked my grandparents a HOU-LGA flight for something like $160 r/t all-in ).