I think it depends. This OP says the LT booking would be $30k, which is can be a substantial sum for many, or the host may have plans change and need to be away where the LT booking will be easier to manage remotely.
So long as the cancellations are handled with the utmost respect and help given to find a new accommodation, say even a financial perk of some $ for the trouble, then I think it is acceptable…in extreme cases.
As a GENERAL RULE though, once a reservation is accepted, a host should honor it and take it very, very seriously.
We have had a couple of guests who had been cancelled on by hosts (even at the last minute), and were left high and dry, which makes hosts look terrible and is a deterrent to new potential home vacation renters. But we also once had a plumbing emergency that ended with unavoidable cancellation(s) and Air was extremely helpful in “re-homing” our booked guests. We felt terrible, but that is how it goes sometimes. Hotels and airlines ROUTINELY OVERBOOK and “bump” people, leaving travelers scrambling. A higher standard should be set for home-sharing imo, but it may be the exact opposite. I don’t know the [comparable] stats.