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.
I think this is the main reason for online streaming only: Sailor Moon Crystal is not expected to make money among the Japanese, so its only hope to turn a profit is to make it available to viewers outside of Japan.
The classic anime series aired on Japanese television and garnered many fans inside of Japan, so tons of merchandise was sold to little girls. The reboot is not airing on Japanese TV; it is streaming on a website called NicoNico Douga.
In Western countries, streaming technology like Hulu and Netflix is hugely popular. In spite of the rest of the world’s image of Japan as technologically-savvy, a large number of Japanese young adults are virtually computer and internet illiterate, only accustomed to using mobile-friendly websites on smartphones. Among all of my college friends here in Japan, I have only met one who had heard of NicoNico, and none who have heard of Hulu even though it exists in Japan. If not even the college crowd knows about NicoNico, I can guarantee you that the older generation and the shrinking birthrate’s Japanese kids aren’t aware that the reboot exists, nor would know how to access it even if they did. The average Japanese family won’t huddle around the TV set on a Saturday morning to watch the next episode of the reboot, like they did for the classic series in the 90s. This means that the entire Japanese viewership for the reboot will be the middle-aged otaku who’ve stayed fans for 20 years. Director Munehisa Sakai specifically said, “We want grown women who watched the original anime to watch this!” Well, I am a grown woman who watched the original anime and who is living in the Japan, but I really don't want to fork out to buy a monthly subscription to NicoNico just to watch 1 show that only airs 1 episode every 2 weeks. If they had wanted to attempt something of a substantial Japanese viewership without airing it on TV, they should have at least put it in the Japanese Hulu (hulu.jp), but they didn't.
The chance that the reboot will draw in new Japanese fans is unlikely. And the chance that the legions of Japanese young adults who avidly tuned in to BSSM as kindergarteners back in the day will even realize there’s a reboot is unlikely.
Consequently, the reboot is not very marketable in Japan. Some new merchandise is being produced, but the sales numbers will be nothing like the boom in the 90s when thousands of elementary school girls across Japan were buying the costumes, transformation toys, dolls, stationary items, picture books, paper dolls, coloring books, etc.
The Pretty Guardian Sailor Moon live-action TV series did air on Japanese TV and did produce a collection of merchandise marketed to little girls. Even so, it only ran for one season: the Dark Kingdom arc.
When I first heard news of the reboot, I wondered if BSSM might possibly come back out of the woodwork and give the Pretty Cure franchise a run for its money (this would be a considerable challenge, since Japanese kids may have heard of BSSM but haven’t watched it at all, whereas they’ve grown up on Pretty Cure, and PreCure is able to switch in and out the character types in each incarnation of the series, keeping things fresh yet familiar. In contrast, BSSM is one long tale with the same core characters throughout, less up-to-date, and less child-friendly. But soundly thrashing PreCure wasn’t a total impossibility). However, I can safely say that Pretty Cure is firmly holding its ground on the airwaves and on the shelves of the toy stores, electronics stores, 100 yen shops, everywhere in town. I’ve only come across 20th anniversary BSSM merchandise in a clearance bin in one store. Not even Animate, the main anime merchandise store, has any Sailor Moon Crystal merchandise in stock.
The reboot anime is 26 episodes long, period. Those 26 episodes are scheduled to be released over the span of a year, one every other week. The series would need to be renewed in order to run past the first story arc (Dark Kingdom) in or after 2015. It’s possible that it could get approval to be extended, BUT the situation is very different from the classic anime series’ run.
If the reboot gets extended, it will need to be based on the marketability abroad: the international BSSM fan community. How many of you are planning to import reboot merchandise from Japan within the next few months? If you aren't, then I'd warn against expecting to see further seasons produced.