Most of the smaller advanced countries do have better service and better phone systems. That is a fact, the reason. The size of the United States.
Because of the lower urban density and the fact a large fraction of the US population lives in rural areas, the result is that the US telcos like AT&T, Verizon, etc. have to deliberately limit their speeds to make longer-distance connections possible. Right now, I'm running EarthLink ADSL at 6 megabits/second download/1 megabits per second upload, mostly limited by the DSL capacity on the AT&T lines.