If I remember my Economics studies your argument applies to a free market. But broadband companies have a very large initial capital investment which raises the

If I remember my Economics studies your argument applies to a free market. But broadband companies have a very large initial capital investment which raises the bar for entrants. For wireless you also have a limited number of frequency licenses that limit supply. And when supply is very limited, and you know that it will be very very hard for anyone else to enter the market, then you oligopolies can appear. That said, I don't know the USA market enough to say if they currently have a monopoly or not, or if they are colluding or not.