Why is Sailor Moon (2014) not airing on TV? The new Sailor Moon seems to be showing on Niconico exclusively. Why would it not air on TV, or both?
Like senshin mentioned, nobody really knows for sure. One possible speculation floating around is if Toei has another series on TV in July (Say, Precure or Dragon Ball Kai) they wouldn't want it to compete with Sailor Moon Crystal...but even that explanation doesn't make much sense.

Most likely, streaming Crystal on an online service such as NicoNico is the easiest way of reaching an international market, since NicoNico will be streaming SMC with 10 different subtitled languages available. Online streaming could be the easiest way for Toei to keep track of how well Crystal does (internationally and in Japan), either before creating more seasons or airing it on Japanese TV.