Interstate commerce is governed by the federal government. The internet is a bastion of interstate commerce.
Schools now require the internet for kids. ISPs being allowed to be anything more than a dumb pipe means they have the control of what information is sent across their network.
The internet is now a basic human right in the United States for numerous reasons, one of which is #2. Basic human rights have notoriously been mishandled by the states. See: slavery, indentured servitude, civil rights, voting rights, air and water treatment, etc.
ISPs cross state boundaries and should be governed by interstate law.
An ISP being a business, especially a publicly-traded one, will sacrifice all manner of consumer/user-protection in order to maximize profit. And having the states govern against that will lead to a smattering of laws where it becomes muddy on what can actually be enforced, and where.
Net Neutrality, as a general concept, must be codified into federal law in order to help protect the common good and interest of such a basic utility – and yes, the internet is a utility despite in some places, very few in fact, where competition is available.