"what am I doing wrong" is probably a better way of putting it.

I tend to get romantically interested in people I already know quite well, which would work against getting together with such people. I find consciously flirting really hard, and I'm not sure that it's not been counterproductive when I have tried it. But keeping in this pattern isn't going to help loosen me up, unfortunately.

Your last point makes a good deal of sense, but by the time I dare even broach the question I am already far too emotionally involved for casualness to work. Maybe this puts people off.