ISPs compete on the basis of their ability to provide residential bandwidth at competitive prices:
Suppose one ISP offers 1 Mbps up and down for $99 per month and another ISP offers 10Mbps down and 0.25 Mbps up. Both of these plans may cost the same to provide. Similarly, a 0.5 Mbps dedicated bandwidth circuit may cost 2x or 3x the cost of the residential circuit to provide.
Individual ISPs determine what markup to apply and how to price the bandwidth (with or without contracts, etc.). You are arguing that all circuits should be dedicated bandwidth circuits. There is nothing wrong with that argument, but it reduces the value of every piece of copper or fiber in the system because it prevents it from being maximally utilized.
Also, keep in mind that if a law were passed requiring all circuits to be dedicated bandwidth circuits, ISPs would have no incentive to preemptively upgrade hardware. Notice that customers do not demand symmetric dedicated bandwidth circuits. For most residential customers, only a minimum amount of upstream bandwidth is needed (for ACKs and the occasional upload) because most of the data is flowing to the customer and being watched on a screen.
T-Mobile's "Binge-on" service is a brilliant way of applying QoS to consumer demand to extract more value from the network, yet it was criticized as non-neutral. It's amazing the level of misunderstanding that is attached to net neutrality!