Cable stocks have fallen sharply and most trade near 52-week lows, but that is not keeping short sellers from continuing to believe that they could go lower. The short interest in Comcast (NASDAQ: CMCSA) and Charter (NASDAQ: CHTR) went up on December 14 compared to November 30 according to data from Nasdaq.

The slide in cable shares began around mid-year, when comments from Comcast indicated that the new TV-over-fiber products from telecom companies like Verizon (NYSE: VZ) were starting to take cable customers. Up until recently, cable was able to market voice, TV,and broadband as one package into the home. The telephone companies could not match that. But fiber installations have changed the picture, and competition is fierce.

Cable companies are starting to see slowing growth in their subscriber bases. That could push them to drop rates, and it is forcing them into capital expenditures to improve the speed of their own networks. Both moves put pressure on earnings.

The big bet against cable may be premature. It will still take years before telecom companies can get fiber to all of their customers, and there is no guarantee that these consumers will switch from cable. Also. cable continues to take a large number of voice customers from the telephone companies with inexpensive VoIP products.

Cable may not be dead yet.

Douglas A. McIntyre is an editor at 247wallst.com.