Question: If Comcast is such a monopoly that everyone here keeps repeating ad nauseam, why hasn't it been broken up ATT style yet?

AT&T was broken up into a bunch of smaller regional monopolies that did not compete with one another. (Almost a century after its founding, by the way, and decades of on-and-off litigation.)

The cable industry has evolved into a bunch of regional monopolies that do not compete with one another.

The effect of breaking Comcast up AT&T-style would be... a bunch of regional monopolies that do not compete with one another. And then, as with AT&T, proceed to consolidate via M&A into larger regional monopolies... that do not compete with one another. Same as now.

Welcome to the American telecommunications industry.

That doesn't discount the fact that laying cable costs lots of money is a natural monopoly.

Wait, so in one post, you challenge HN's readership to prove that Comcast is a monopoly, and then two posts later you assert that cable is a natural monopoly. I'm confused what point you're trying to make.

Comcast is a natural monopoly, and there isn't anything wrong with that. Competitors are free right now to lay cabling to areas where Comcast already serves, they just choose not to because it isn't a smart financial decision.