This question comes up time after time and winds me right up, along with the 'rescues make loads of money, getting dogs for nothing and selling them on' quote.
Many people successfully adopt dogs. Most rescues work on a dog-by-dog basis so that being turned down for one does not necessarily mean you will be turned down for another.
When it comes down to it, the rescue has a far more realistic view of the chances of a successful adoption than the potential adopter, because the rescue is dealing with the results of failed ownership twenty four hours a day and seven days a week. They know exactly what they don't want to happen next.
They don't want to add the upset and trauma of a failed adoption to those of failed ownership; not for the adopters and certainly not for the dog. They want to get it right first time so they can go on and help another dog.
No potential adopter ever thinks they could be anything other than the perfect home and even going by the law of averages, let alone probability, this can't be true. Neither does the perfect dog exist.
Rescues have heard all the good intentions. They've also heard all the excuses. They develop a sense of which potential adopters will stay true to their intentions and which won't. At some point, a line has to be drawn, under which applications will be turned down.
Blanket bans are actually pretty rare and when they exist it's for good - and mainly safety - reasons. Sometimes it's for ethical reasons. A rescue which is anti-hunting is unlikely to re-home a dog to somebody who might hunt with it, for example.
Most rules come about through bitter experience. If you read through 'The Doghouse' here the same issues come up time and time again and it's the causes of those issues which can result in potential adopters being turned down. Just because you know someone who managed perfectly well in those circumstances does not mean everybody else - or indeed anybody else - will. The dog they apply to adopt may have come from just such a problem. There has to be a lowest common denominator.
Sure you can buy a pup from a breeder but (a) there are far too many pups being bred for far too many of the wrong reasons by far too many of the wrong people and bought in the wrong way, despite the advice plastered all over the place and (b) you still don't have a guarantee that the pup will turn out how you want. It might still grow up and bite your kids or chase your cat.
You could also buy (not 'rescue', please: buy) a dog from Gumtree, or similar. If so, please get very good at reading between the lines of the adverts, because you'll have no back-up. The number of calls rescues take from people who have 'rescued' a dog from Gumtree etc. but 'can no longer keep it' is enormous. Many poor animals go round and round the internet sites, getting more and more damaged each sale. You might be lucky, of course...
To buy a pup from a decent breeder might involve waiting and will almost certainly involve lots of questions from the breeder, possibly a homecheck, to see if they think you're suitable.
To get a dog from a proper rescue organisation will involve questions and homechecks also. You might need to wait for the right dog if the rescue doesn't think you're a match at first try.
Or you can cut corners either way and risk increasing the rescue burden, whatever.