Why does Cablevision want your Social Security number?

I'm getting killed with the cost of my Verizon FIOS service, partly because of all the "tax".  So I just tried to switch to Cablevision's Optimum service.

I started the order process on the Optimum website but that would not go through and I had to call.  We didn't get very far.  The order taker wanted my Social Security number.  The explanation was security, that someone might contact Cablevision pretending to be me and try to cancel my service.  I said there were other ways to provide that type of security and refused to provide my Social Security number.  I also asked if it was for Cablevision to do a credit check but that was denied.

I figured Cablevision would fold and place my order anyway but that did not happen.  I was told to call back if I changed my mind.  I said likewise and hung up.

Cablevision actually lost a new customer over this.  Why would it be so important?  Certainly not to provide security to either the company or to me.  Probably to chase people to collect unpaid money Cablevision thinks it is owed.