The reason for this is primarily a technical one, not a policy one. There's no policy that says the electric company can't degrade all the electricity in your house that's not being sent to GE appliances. It's technically impossible given current infrastructure.
The internet, particularly across the span of an ever-changing ISP space, networking standards, extreme growth, etc. - the ability simply didn't exist to do what can be done today in traffic manipulation. We're not talking about "your IP is X and Netflix is Y and we're slowing it down" stuff. We're talking about network appliances that can dynamically inspect packets for content and alter the routes which those packets take in real time. Five or so years ago reliably streaming something at an HD resolution to millions was borderline impossible, and the network protocols and software updates to make that happen were racing with hardware to keep pace.
Around 3 years ago depending on who you ask, they basically caught up, and what was previously advanced security hardware (and incredibly expensive) became commodity networking capabilities. If you're in the industry, those capabilities alone demanded net neutrality laws. Before the Comcasts of the world had even figured out who or what they would do with packet manipulation, everyone knew the potential for it and that there really weren't any scenarios that would favor the consumer (overall congestion is a red-herring - that's basic stuff managed through pricing tiers and overall traffic monitoring/switching).