True, there is only one cable running to your house. But it is your local Government that decides who can use it. Many jurisdictions demand competing providers for the citizens. That is why many jurisdictions require cable sharing. That means, for example, if Comcast actually ran the cable, they still have to allow other companies to use the same cable after paying an access fee. The company paying the access fee still has to comply with PEG, and get issued a certificate of public use. But this process still allows multiple cable providers to serve the same home.
You seem to direct your distain at the cable companies instead of the real culprit, the local Government. A cable company cannot run cable without a certificate of public good. The certificate is needed because the companies are using public right of ways, and in exchange for that access, they must provide PEG (Public, Educational, & Government Access Television) channels. It is the local jurisdiction that got together and voted on only allowing the one provider you had. They don't want ten companies running ten cables down every street.
So you do have a recourse. You, and a small army of like minded individuals, simply lobby your local commission to have the cable company changed, or a new one added. It is the commission that controls the monopoly, not Comcast. Of course the commission will probably not want to give up the big fat Comcast contributions, but that is a subject for another thread.