Why do rescues make it so difficult to adopt dogs?

Why do rescues make it so challenging to adopt a dog? After all, don't they advocate adoptions? These questions seem to be arising very frequently in the world of pet rescue today. People all over the Nation are sharing their experiences of how difficult the process was for them to adopt their dog, many of them who moved on and purchased pets from pet shops or breeders. Are we turning away great homes? Well, one may argue that. However, working with different rescue groups, and more so, rescue dogs... we have seen so many dogs get repeatedly abandoned or surrendered mainly because the pet parent did not do their homework before hand. These dogs, who already had a pretty unfair start to life, have continued to be exposed to a lifestyle of being treated like waste... disposal. Some of the very common reasons people surrender dogs are: 1. People move 2. Lack of training, therefore behavioral management issues 3. Puppy grows up, and is much bigger than what the family expected 4. Family is expecting (human baby) 5. Life! Challenges! Changes! Unfortunately, the animal is always at fault, and the one to suffer. People seem to have all sorts of ways to talk themselves out of this commitment for life, the most popular one being "I feel so bad for the dog, I want to find him/her a home that can do more for him/her." Again, pushing the responsibility of commitment over to someone else, and who does it fall upon? People who work in Rescue! Rescue groups or Shelters. Day after day, they bare the agony of devoting their lives to the animals that someone else originally made a commitment to and then changed their mind. They face dealing with reason after reason, story after story, and see dog after dog that went uncared for, neglected, abused, and abandoned. They invest their own resources; and I am not referring to the monetary resources that others have contributed towards. Their own time, energy, body, blood, life. So, this still does not answer the question why they make it seemingly so difficult for people to adopt from them. Well, for many reasons, but the most important one being, that they do not EVER want to see their dogs back... not to their rescue or a County Shelter, they want FOREVER homes. The work is so crucial, and they are outnumbered. Resources and time being so limited, and no one to throw them a bone (a break)... they have got to keep going. They are on a mission, and that is to find every dog (pet) a forever home... Again, Why then do they make it so difficult to adopt, turning down great families? The anser is simple. Even the greatest of families fails to have learned the greatest lesson in life. And that is, through thick or thin, we shall remain together. The hardest part of rescue is putting your trust in someone you thought was so perfect, and then you learn the truth. For this, rescues attempt to prescreen for all possibilities of it not working out... is this wrong?