This really isn’t the right question. The better question is why Congress hasn’t codified net neutrality into law, which is what the FCC has been asking for at least a decade if not longer.
In some ways, it’s better that the FCC can do this without Congress. But it leaves it open to the next republican president to just do away with it.
Given some states barring porn, it actually be interesting to see if other states like California start codifying NN into law, forcing companies to adopt a patchwork of laws. Typically the loss of money motivates them to lobby Congress to do the right thing.