Having to be on chronic medication for life.... some of these medications for things like epilepsy, severe Leishmaniasis, heartworm and injuries are expensive and of course, the dog requires ongoing Vet checks and testing throughout its life.
n be extremely expensive, for conditions like long-term Lei
Unfortunately, some of our residents have socialisation/behavioural issues which can be quite severe.  In these cases. there's sadly no option to rehome. 

Where dog has suffered severe abuse, (physical and/or mental), they suffer terribly with severe anxiety, it's cruel to subject him/her to the change involved in rehoming.