"Triple Play" packages from the cable company… is it a scam?

I currently get Cable TV and Internet through my monopolistic local cable provider. They will charge me almost half the amount if I add the phone. How is this possible, and what is in it for them? They push this package so much and even spam my phone trying to get me to switch.

Have you ever had the “Triple Play”? Are there any hidden fees or taxes? Do they push it because then the government gets added tax revenue and so the cable provider gets more subsidies? What’s the catch?