Sure, I meet marriage quality girls all the time. Look, guys try to make women so complicated when they're actually not at all. At the heart of every woman are two basic needs. The first is the need to be listened to.
What's really confusing for most guys is when his girl starts inexplicably doing strange things that cause the man to mumble WTF?? Where did that comment/action come from? Women start doing crazy things when their emotional frustration builds up. This frustration may not have anything to do with you. It could be something a friend of hers said to make her feel insecure, or perhaps she's in a tiff with her sister and it's bothering her. These are the times that she needs her first need met. By you asking, "Hey what's on your mind? You seem a little down today.", you've just enabled her to dump emotionally and get everything off of her chest. But here is the key...... She's not looking for a solution to her problems, so don't listen solely with the intent of problem solving. That will only annoy her. All she wants is for you to listen and show some interest in what her current problems are, not fix them. Give her that outlet when she needs it, and quickly she'll turn back into her normal self. Neglect her desire to be listened to, and she will continue saying and doing weird things to get your attention.
The second desire she has is the need to feel secure. If you can meet her basic needs in that way, then she will meet all of your needs. The problem is that many guys are looking for a girl who can actually take care of herself. Even if a woman has the ability to take care of herself financially, it's not the optimum scenario for her. Why? Because when she takes care of herself, she's always having swirling thoughts about what would happen if she lost her job, or got hurt, or whatever. But when the man provides his girl with security, it releases a ton of worry and anxiety because now she has somebody in her life that is really stepping up for her. And if she chooses to continue working, she will enjoy her job at a level she never experienced because she knows you have her back no matter what.
So the question is not whether girls are marriage quality or not, it's really a question of whether you can meet their two basic needs. If you can, then she'll be everything you want in a woman. If you can't, then you'll be like so many other guys who are either stuck in a bad relationship, remain single, or just date around moving from one girl to another wondering why none of those relationships have really worked out.