Basically the same as insurance. If you use it once or twice it will probably pay for your premiums for years to come rather than money out of your pocket today. If you never have to use it, then money lost.
Convenience. One call and they will take care of everything for you. And they already know tow services capable of handling RVs. And some, such as Coachnet, offer technical assistance over the phone.
But with smart phones and the ability to do internet searches even in the boonies (if you have decent signal strength) it is pretty easy to find services yourself.