One of the key reasons the net neutrality fight even became a thing was widespread concern that big ISPs would abuse their power to behave anti-competitively, picking winners and losers across the internet ecosystem, and nickel-and-diming consumers in a variety of obnoxiously creative ways.
Verizon, for example, charges you extra if you want 4K video to work properly. T-Mobile spent years letting some key partners and services (namely large companies) bypass usage caps and network throttling restrictions.