It could have gone back to Congress to get clearer statutory authority for its mandate to regulate the web. If successful, that effort would have led to a solution in the form of a new statutory provision that carefully defined what the FCC could or couldn't do in regulating the internet. While that would have been an ideal solution, it would have meant having to get support for the agency's net neutrality goals in Congress, and that support was doubtful.
The other choice was to do what it did here, and that is to take its existing authority over common carriers in the telephone market and attempt to extend it to the internet. The problem with this is that such authority is very broad-based and includes (among other things) the power to regulate pricing through a complex system of tariffs.
The FCC is claiming to do a "hybrid," however, by saying that, yes, we are going treat internet access providers like phone companies but we don't intend to regulate their pricing or exercise any of the other broad regulatory powers we might otherwise exercise once we use this this approach. In effect, the agency is saying, "we plan to come in with a scalpel and do only what is needed to implement our narrow regulatory plan that is focused primarily on net neutrality rules - so, don't worry about the rest, trust us that we will not overreach."
Of course, nothing is in place under the FCC's chosen approach to stop overreaching by the agency except its own discretion. By invoking existing statutes designed for another purpose altogether, instead of seeking to get a new statute from Congress aimed at solving the immediate issue of net neutrality only, the FCC is exerting government power in a way that may not have been contemplated by the original statutes and in a way that will most certainly be challenged in the courts.
Maybe this approach will work for proponents of net neutrality but it comes at a price of the government staking out a pretty broad claim to regulate the internet without any particular checks on that power beyond the FCC's own judgment as to what it should or shouldn't do in the future. Thus, this is basically an agency power grab - perhaps supportable, perhaps not - but almost certain to have unpredictable and potentially unpleasant side effects as always happens when there are insufficient checks on government power.