Competition will drive down prices, increase speed and result in the best possible customer service!
Except that in markets with expensive outlays to get started that rarely happens because the expenses put a natural limiter on the amount of people that can actually mount competition making that number low enough that the competitors can essentially carve up the market, price fix and then all suck approximately equally, indefinitely. Just like ISPs and cell phone carriers do now (and will continue to do so until the government steps in and forces them to fix their shit).
In regulated markets. After all, things like anti-cartel laws are regulations, and we absolutely do need those.
Not to mention that municipalities compete with one another; it is actually easier in most places in the United States to move to a neighboring municipality than it is to switch to a better ISP. For example I would have to move over a hundred miles to get better internet access than the large, regional ISP that serves my area, and meanwhile I could move about five miles and "technically" live in a different city in the same metro area.
Finally, I am not advocating municipal control instead of private ISPs, I am arguing municipal offerings in addition to private ISPs. It is tautologically impossible for the introduction of new entrants into the market to itself constitute a reduction in competition.