Reason why the monthly schedule is still hidden?

That's an option.
Maybe they didn't want to make a scedule for around the 3.0 update and now thry don't bother making it for the half month we have left.

I don't know why they are holding the calendar though, but I have a feeling that things aren't going as planned lately.

3.0 seems to have caused them some delays and they don't know when stuff is going to be ready.

I mean, I can't be the only one to think that AR was meant to be released with 3.0 and the Mythic heroes, but they ended up releasing it early due to some internal problems.

Eir would have been the third hero in Fire and Ice banner. Instead we've had this weird new hero banners (2-man one, no new heroes now but a hero fest). It doesn't feel right.