@Lianne24 you seem to not recognize that these properties have cancellation policies (you say it is a change, but really you are cancelling first dates and re-booking new dates). and those cancellation policies exist for a reason.
Changes such as yours are a reason why 1)some guests would buy trip insurance or 2) some guests would be sure they can indeed travel before they book travel or 3)some guests would make sure that the cancellation policy of the place matches their needs.
As it is now, you booked a place and prevented that host from taking other bookings from other guests during those dates. Now that some part of the travel that you are responsible for is now not available you would prefer that the host be inconvenienced rather than you being inconvenienced.
How is this right??
The host offered something: certain dates at a certain price with a certain cancellation policy and you chose to buy it. Now later you would like to change the deal.
No one likes to "waste" money, but in this instance you seem to think that the host should be out more than you and that doesn't seem right.