You should see the mess we have in Australia. I think most people churn every 6 months as every ISP does the same stupid 30% off for first 6 months deal.

It's all the same national network so there's very little difference between ISPs.

It has more to do with the cost of accessing that network.

Bevan Slattery used to do a yearly Commsday presentation where he would tear the NBN economics up live on stage. Basically after getting the service from NBN to the provider, theres basically nothing left over for the provider to use for support, transit, peering, hardware whatever.