Yes, you clearly don't understand the problem.
Arrival or departure are just one of several reasons instant book should be customizable.
In your scenario, I must lose money, by not allowing a day to be booked altogether, when what I am asking is that I be able to deactivate instant book for certain days, thus necessitating that a guest must first get my approval -- and if necessary, be notified of certain changes which may affect their arrival (or not) -- before being allowed to instantly book...but I CAN STILL RENT THE PROPERTY.
For a property where I book 26 nights a month, I'd say, on average, this allowance would apply to 4-5. You're asking me to forgo income on those nights by making them unavailable altogether, rather than simply requiring that a little communication take place to ensure that both the hosts and guests have the best experience.
As it is on Airbnb now, it's all or nothing...which means that both Airbnb and I lose money, which isn't just bad business. It's stupid.