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.

If someone had a stable low price they'd just keep customers for longer.

I can't imagine high churn helps anyone.