With girls met online. I have noticed that people make one very big mistake. Their online personality does not match their real life personality. That could be one cause of the issue. I know I watched a former roommate do the dating site thing. He was lucky to get 3 or 4 dates, his average was 1. Just because it looks good on paper does not mean it will work.
A male specific issue, you treat the female like she is your buddy and not your lover. You need to give females something intimate so they can feel special or connected to you. You need to make her feel like she is a mate, not just a friend. You need to turn her on. If you fail to do that you will stop looking like a potential mate.
Male specific issue number 2, you are boring. It is a fairly well established fact that females tend to get bored of things quicker than males. So if you are boring you will lose her interest as well. Boring is not fun, females like to have fun. Most boring people are not fun people. You strike me as someone who is very boring. One thing you must do as a male is lead the female. Maybe she has no interest in a museum. It is your job to make it exciting for her. Just because you are excited and having fun that does not mean she will have fun. If she is not having fun, that is a turn off.
Male specific issue number 3, you are all there. One thing females like is mystery. Have you ever noticed how girls date jackasses who are clearly jackasses. If you talk to them they generally say something like There is just something about him. You know mystery something she cannot quite put her finger on. If a female feels she has met you and figured you out. Well then there is nothing left. Mystery is exciting, and fun.
Male specific issue number 4, you are no challenge. You are a nice sweet guy and that is great. However, that is also boring. You have a couple of dates with her and she already has you wrapped around her little finger. You come at her beck and call. You have committed to her long before she commits to you. She does not have to try to get anything out of you. Boring, not fun she doesn't feel like she has earned her place as your mate.
Male specific issue number 5, you do not have many options. Females want to be the envy of other females just as much as males want to be the envy of other males. There is such a thing as being too available. You have to walk the line though. You need to seem like you can replace her if she were to leave you. If you come off as desperate at any point, well... yeah that is a turn off.
General issue, you are closed-minded. I often times see on this forum I hate bars or Clubs are full of idiots or stuff like that. You know that is just fine, that is not your scene. However, that does not mean your chosen mate does not feels the same way. Maybe your mate wants to go to a night club to dance with her man. Maybe she wants to show off her man to all those club friends of her. So yeah you may not like the club. However, if you just flat out reject the idea or activity... well you are digging your own grave. Because you are insulting her interest. Remember, you are a part of her life and she is a part of yours. If you are turned off by a big part of her life, no matter what it is, she will be turned off of you. There is no way around it. So open your mind and get out and try something new. Have an experience that you can share with him/her and that will bring you closer.
General issue 2, you are not driven. This applies more to males than females, but it can ring true for both. While this is kind of a vague idea. If you seem content you will probably turn off your potential mate. Be a person in motion. When you finish one project start the next one. Do not stagnate as an individual. Start a project or an idea with your mate. That way you can build memories and intimacy together.
I love how guys who are nice feel they are persecuted in real life. Being a nice guy is great. However, if you are unattractive, inattentive, and worst of all do not make her feel special.. well hey that is just going to screw up your chances. Stop being a diamond hidden in the rough. Be a jewel that is on the concrete. Stop playing into the stereotypes set by the media. You can be the full package if you let yourself be. What kind of female does not want a handsome, charismatic, fun, nice, loyal guy?