Sometimes when you contract out, the dynamic is what you suggest, the contractors are incentivized to do good work lest another contractor get their business.
And by "good work", I mean "cheap". Trust me, Comcast does not give a single fuck about the quality of work these contractors perform, so long as the price is right. Even the occasional rework (due to those whiny customers who actually want what they're paying for, the greedy bastards) still leaves the overall scheme profitable.
I've met Comcast contractors who were quite good. Quick, professional, polite. I've also met Comcast contractors who were drunk on the job.
The one saving grace here, if there is such a thing, is that many contractors prevent one from becoming so entrenched in one area that Comcast has to do business with them, because there is no competition. (Karma's a bitch.) A private company runs our water service here. While the rank-and-file employees are competent and professional (at least the ones I've met, who once had to repair our water supply line on Christmas Eve), the management is rotten to the core. They ignore mandatory aspects of the contract with the town, like routine maintenance requirements and disaster plan documentation available on-demand by the board of Selectmen or its designate. (They're also supposed to have enough reserve capacity so that if one of their pumping stations breaks down, the remaining equipment can handle the load. Nope. A while ago when a pump failed, the town was notified, which is a small miracle in and of itself, the town had 3 hours of water left. There were no repercussions from this obvious incompetence and breach of contract.) We had a boil order for 11 days a few years ago, because lack of maintenance on a storage tank led to a cryptosporidium bloom. In this state the way you get a boil order lifted is by having a negative test for the infection two tests in a row (twice daily), with the test performed by a lab the state specifies. One of the managers of the company took a sample, dumped bleach in it, and submitted it for test. This was, of course, immediately detected by the lab, since 1) the chlorine level was off the scale, and 2) it changed color unexpectedly when the reagent was added to detect the infection. That manager went to jail.
Of course, the private company immediately lost the contraHAHAHAHAH couldn't keep a straight face. Of COURSE they kept the contract. They own the lines. They have a monopoly on the water service in our town. The customers have no say in how that company is run, whereas if the town ran the service like nearly everyplace else, they could at least vote incompetents out of office. They had the balls to ask for an 83% rate increase a couple years later. They got 33%. The town basically had no choice, if they wanted to continue to get water service.
When private companies have no incentive to provide the service they're being paid for beyond losing the contract, and they are the only game in town, they don't lose the contract. They can pretty much do whatever the fuck they want with impunity.
Privatization is not a cure-all. Given the choice between a private company and public administration for a vital town service, I'l take the (unionized workers from the) town every time.