PON cuts the number of feeder fibres by orders of magnitude. GPON is typically deployed with 1x32 PLC splitters. With XG/XGS-PON deployments with 1x64 and 1x128 splitters are feasible. If you have infinite financing, sure, more fibres are better, but in the real world there are significant cost increases with higher fibre counts that not all providers can absorb. Municipal entities can easily get 30 year amortization, which is definitely not the case for most startup ISPs in unserved markets.
