All of them are shared one way or the other. A dedicated line costs in a range (10-100x) that only huge commercial entities can afford.
Normally there is a pool of bandwidth with a lot of users, a limit of users is fixed upon it which is normally termed as the contention ratio. There are other controls which modify this limit with respect to usage. Also controls which will shift high traffic users to other pools with less of the same.
PTCL has a minimum ratio of 5-10 connections per connection type. Don’t know about these fiber networks.
So there is a possibility that many/most of the users are high traffic ones. They will bog down the system by filling in all the pools and force the load balancers to operate on the minimum quality levels configured. Thus essentially removing the balancing effect and resulting in network congestion.
The more active high traffic users, the lower the speed in peak times.