Why do women react negatively when a guy is nervous?

I'm 23M and have social anxiety, I've had a horrible (almost nonexistent) experience with dating. I've always been afraid of approaching or flirting since it's ended badly in the past.

What I'm wondering is, why do women dislike when a guy shows he's nervous? Why does a guy have to be smooth or have game anyway? One response I read about this was "If a guy is smooth enough to treat me like a human and not some intimidating scary alien, that would be good." Why is that the correlation? Why is it such a turn-off? Why is confidence so important? Do women see it as a red flag to be this old and still nervous/inexperienced?