Yes, but.... it's like those cars that run on used french-fry oil. It's really cheap so long as the demand side stays within the existing production quantities. Once the user base increases, however, the demand for used french-fry oil far outstrips the supply, and prices go up.
Same thing here: the companies in question are almost certainly hooked up to natural gas lines, which take care of heating and cooking needs. That's fine, if you're one of a very few who are doing it ... but once you get thousands of users, the supply chain for natural gas turns out to be completely inadequate and, again, demand outstrips supply and costs go up by a lot.