I think the problem with all of You is that You're insisting on using the gregorian calendar. Said calendar was introduced by Pope Gregory XIII in October 1582 and it's a little outdated.
With the requirements of the modern Short Term Rental business it's important to have as many days as possible to rent in a month. Airbnb realised that and is obviousely using an updated calendar version with more flexibility in terms of the numbers of days in a month.
Picture this: What if we had 100 nights to rent in a month, that would boost our income considerably. Don't be negative, see the advantages of the new system.
Airbnb is an innovative and host-centric company and their main objective is to work for our benefit.
Crazy! I often receive emails from airbnb for nights i could have booked for lower price, but the point is the whole month is booked already.