If I understand things somewhat correctly, it did pretty good business, especially overseas, but it wasn't enough because of the overinflated budget. If it continues to do well in Drive-Ins, dollar theaters, DVD and cable, I don't see why they wouldn't produce a more reasonably budgeted sequel. Studios love franchises.
Studios abandon intended franchises all the time. As for the film's "pretty good business," it did horribly domestically (the film won't even reach $75 million by the end of its run) and was, at best, unimpressive outside of the United States (between $188 and $210 million).
Also, ask yourself when a franchise sequel cost less than its predecessor and you'll have a pretty good idea why John Carter (which had a colossal production budget reportedly between $250 and $300 million; this doesn't account for prints and advertising) won't be getting a sequel.