Host cancellation does carry severe penalties @Robert9726 , and I fully agree with you that it should (barring a catastrophe).
1) The host is fined
2) The dates remain blocked on the calendar and cannot be opened
3) If anything over 1% of total bookings get canceled, the host doesn't qualify for Superhost
4) The listing has cancellations recorded against it, which hurts its search rank.
If you say you see many hosts canceling, I assume they won't be around for long.