So what are they using? Mobile phones--Pew says 20% of adults do not have broadband at home, but own a smartphone. Or nothing--Pew reported that 11% of U.S. adults do not use the Internet at all.
I don't even have working voice cell coverage at my house, much less data. Again, almost certainly due to a an entrenched monopoly limiting the market outreach of competition, and thereby obviating the requirement that they themselves perform adequately enough to retain customers.
Q.E.D.
The only other way to get your math to work out is to assume that only a very small portion of Comcast’s footprint has no other cable/fiber competitor.
As to your cell situation—what mechanism do you think creates this competition-limiting monopoly? And why doesn’t that same mechanism apply to say my house (in the DC exurbs), where all of the big 4 have a decent signal? (Or the majority of the country, where at least three providers have coverage?)
Not saying much at all there.