Originally Posted by ultimatemegax
Kadokawa has bought shares of Niconico and coincidentally publishes those three series. You could also make an argument for Mirai Nikki being somewhat included since Niconico was a sponsor of that show (not seen the others, so I don't know if they sponsored these three) and it aired on Niconico prior to TV as well (by hours, not seasons). It's likely a strategy to get people to watch them on Niconico, gaining ad revenue prior to the usual methods. Not like it would hurt their sales anyways.
Do you need a premium membership to watch these on Nico? I have one but I'm blocked for being outside of Japan anyway. If so, and if they have a stake in Nico, I guess they could be getting part of the premium membership subscription revenue too.