CVC price gouging.
The key issue is that "CVC" or "backhaul" to an ISP owned DSLAM via leased or owned fiber is less than 1/10th the cost per Mbit that NBN is charging for connection to their last mile infrastructure. ISPs can't afford to allow ANY services to run at fiber speeds because CVC is just so ludicrous compared to what they are paying now. NBN's position on the matter of CVC charges is "fuck you we're a national telecoms monopoly".
There's only one way to solve this, it's for the ACCC to mandate that NBN provide wholesale access to the unlit local fiber loop. ISPs can colocate equipment at every POP so as to avoid ludicrous CVC and AVC charges and offer the world class service that NBN won't provide.