Ladies, why do girls only want to be good friends and not a girlfriend (10 points)?

I'm a 25 year old guy that has been on a number of dates over the last six months with a couple of girls that I really felt a strong sense of chemistry with. However, in all cases they have stated sooner or later that they just see me as a good friend and not as a potential partner. I am not really sure what is going wrong as I've never been in a relationship before. Without wanting to blow my own trumpet I think I treat girls extremely well and will never stop being nice. I wear glasses, am not sporty, don't drink, am shy but try my best to overcome it and maybe one or more of these things are the problem?! On the plus side I am very kind and caring, bilingual, two degrees, very independent, ambitious, optimistic and have a job I really enjoy. Any tips or insight? Many thanks!