There are many considerations, education been one of the first things that comes to mind in the sense that, if people were better educated as to what a pet needs and more responsible about it, there wouldn't be soooooo many homeless animals. But the whole thing goes down to who is making the decisions and that, in a nutshell, is the problem because it's always somebody who simply cannot say 'No' to an animal in need. If they could, they wouldn't have opened up a rescue. And, so, every time the rescue is in fairly good shape financially, an animal shows up that requires something super expensive and there goes the 'good shape'! And there are ALWAYS animals that show up! When I first opened my rescue (which, in reality, was more a sanctuary than a real rescue), I did not advertise it anywhere. The only people who knew about it were either friends, people from my own birdsite or relatives but I still got people contacting me ALL THE TIME from all over the place (I had people coming over from Vermont, Niagara Falls, Maryland and even Florida to deliver their birds - now how can you say 'No' to somebody who has driven hours and hours to bring their bird to you?) and, in a matter of about a bit over a year, I went from a few birds to 240! And this is not my story, mind you, it's every single rescue's story!
And it was the same thing with the dog and cat rescue I belonged to. Everytime we did a big fundraiser and made enough money to catch up with all the bills, something happened and we had to divert part of the money for it or we ended up 'charging' it up to the same vets accounts we had brought down to a manageable level. If it wasn't for the volunteers donating not only time but food, litter, medicines, paint, gravel, kennels, chain-link, bedding, toys, play pens, services, etc. we wouldn't have been able to stay open! It was the volunteers that actually supported the day to day cost of keeping it open - that and donations from two supermarkets (we had bins). The fundraisers were mostly to pay for the vets bills as well as electricity, phone, kerosene for the monitor stoves that heated both buildings and real estate taxes.