From National Geographic:
"An ongoing effort to monitor and actively curb methane would end up costing the companies money, because they would have to conduct monthly or quarterly inspections of well sites, using infrared cameras to scrutinize equipment for methane missions. As a result, most oil and gas facilities would end up spending slightly more than they saved, with companies shelling out as much as $2,500 per well and up to $8,000 per gas plant annually."
http://energyblog.nationalgeographic...y-study-finds/
So, cost.