Why not give it to a rescue then?
Because rescues are full to bursting point with unwanted pets and have waiting lists.
Because some rescues kill them when there are too many or if they have not been rehomed within a certain time, or are at a certain age, or in some cases not viable if they need any medical treatment, regardless of whether they can be made better or not. They just can't be bothered to take the time or spend the money donated, instead paying their directors a huge salary.