Short answer: Sometimes us girls are just really stupid.
I want to be completely honest with you and tell you that I think I know where these girls might be coming from.
For me, and I suspect for many other girls, there is something oddly attractive about a boy that doesn't open up very easily. I think it's because us women crave emotional closeness and the idea of getting emotionally close to somebody who doesn't usually let people in is kind of romantic. It's almost like we see it as a challenge.
But no matter how romantic it may seem, the truth is that us girls really shouldn't let ourselves be attracted to men who are emotionally closed off, because in the end, it's not a quality that makes for a healthy relationship. That is something I have definitely learned with time, and I can tell you that as I get older, the emotionally closed off boys are getting much less attractive to me, while boys who are genuine, open, and honest are becoming seriously hot.
I mean, let me remind you of what you wrote about yourself:
"I on the other hand grew up with two very expressive parents and have always been very straightforward and genuine with others as a result. I've always been grateful I was raised this way as it helps people open up to me so that I can really understand them and help them when they need it."
Well, flip, you sound pretty awesome to me!
It's my opinion that you absolutely should not cease to be emotionally open with girls. No matter what, you should continue to be your best self.
Sometimes, when your dating life isn't going so well, it can be tempting to try to change yourself to what you think will get more people to like you. But that's totally the wrong way of going about it! What you need to do is continue striving to be the best you that you can be. It may take time, but that's how you will eventually attract the right kind of girl, and in the end, your relationship with that right kind of girl will be blessed by your ability to be genuine and honest.
Don't tell yourself that you are defective. I think too many of us here at BYU start to truly believe we are defective when we stay single for a long time. I know because I honestly thought my singleness meant that I was defective for the longest time. But that is NOT what being single means! Being single doesn't have any reflection on your worth as a person and you know what else? Being single for a long time does not destine you to be single forever, either. Starting today, you've got just as good a chance as the next guy at finding someone, and when you tell yourself otherwise you are only hurting your self esteem and your chances!
Keep being the best you can be around girls and keep your head up! Someday, and perhaps someday soon, an amazing girl is going to realize what's up and fall in love with you. In the mean time, just be patient.