Greed?
I don't think it's greedy downloaders to blame - ISPs advertise how simple it all is and how fast the connections are. The tech is sold on that - not continuous connection.
However, the current tech is not the same as before, the kit used to try and maintain speed rather than connection but these days the promise is for the kit to attempt to maintain connection all the time. The boxes constantly monitor line condition and are more likely to drop speeds as conditions vary but don't always raise the speeds if line conditions improve --- you can see line conditions change from hour to hour and they frequently vary due to weather conditions, humidity seems to play a large part in it as it can affect whether a joint goes partially short circuit or high resistance. a lot of it is down to the wires.
What the ISP's don't usually tell people is to drop then router/modem connection for a few minutes and power up again. The kit at the exchange is re-set to the highest possible speed at that point in time.
Even here, 1.5 km from the local exchange with recent main cables and joint boxes, it's not unknown for the speeds to drop when the weather gets very wet but the speeds don't always ramp up again. Power off the router, make a cuppa, power back on, speeds restored.
But, as others have said, there is also the problem of insufficient investment - as the customer base grows the kit isn't always upgraded to meet the number of customers so throttle the speeds and blame it on P2P.
You've still got connection, the ISP is still fulfilling their small print.
If the customers are encouraged by content providers to download all the telly programs they missed, download films for a few days rental and share holiday movies and the next music sensation it's hardly the fault of the customers. we;re only trying to use a service that's heavily promoted by content providers and ISP's.
Doesn't seem much different from trying to drive anywhere -- cars sold on a promise of speed and convenience, roads advertised to be good routes to places and shopping centres and theme parks built for the punters to visit.
But somehow it's always the fault of the motorist for attempting to use these services in the way they are told they can as surprise, surprise - it all fills up with traffic.