Many hosts get penalized for not officially Accepting or Declining Reservaion Requests because they are involved in on-going conversation with guests who should have used the Contact Host link to begin with. Blocking the host's calendar is unproductive and causes extra work for the host and Airbnb who ultimately has to unblock the dates. This is especially true in cases where the host and the guest are in different time zones.
Penalize the host if you want with a low response rating, but blocking the reservation dates just causes confusion and aggravation especially when ultimately the guest wants to book the space but can't because the dates are now blocked.
Clare