^Because Hulu has broadcast rights, this was confirmed by Toonami on their Preflight show back in June 2016 that they tried to get Crystal and were outbid by Hulu and considering that Viz posted the entire dub of season 3 on there (& Yahoo) back in October, not much has changed since.
In the long term, this actually is better overall than any network broadcast could be.
The TV landscape has changed considerably even since Sailor Moon Crystal was first announced. Within the past few years, streaming has replaced cable or even fixed media as the go-to for people to watch shows. Yes, people still watch TV and it will never go away completely, but at the same time the trend has been towards a tailored viewer experience.
It really doesn't matter if Sailor Moon comes on cable TV in the United States, because streaming is how people -- especially those who advertisers like to target -- watch TV now.