People are generally nervous talking to new people, some people just get passed that easely because they are used to meeting new people a lot, those guys generally don't have issues with this and have no issues carrying to conversation forward.
most guys just think they have to say something so amazing because someones of the opposite gender and they just choke under the pressure they put on themselves.
Most guys also think if they'll go talk to a women they'll do half the talking, unless you've actually caught her attention and are at least somewhat interesting they won't do this so they don't get a response and generally run out of things to say.
If your a reactive person in terms of conversation especially you'll notice you'll lack stuff to say because well your waiting on her to say something you could reply on but she simply doesn't do so, creating akward silences.
If the dating scene would be so simple that a women always does half the talking even if she doesn't know the person, this problem wouldn't be an issue as much as it is now.
Most (especially inexperienced) men tend to put women on a pedestal. Men were raised to think that women are princesses and goddesses (it's true!) so men tend to get nervous and anxious when a beautiful girl approaches them. It's the same thing where women were raised to be princesses and get rescued by prince charming and all that jazz.
It's not that men are scared, it's the anxiousness that they feel like they're going to mess up or say something embarrassing or anything else like that.
sometimes guys just feel uncomfortable with things and not ready to talk to the girl , I sometimes feel that and don't feel like talking to her rate away if I don't even know her . if I know her I'm usually pretty comfortable in talking to her
most guys don't have the confidence or experience to carry a good conversation with an attractive girl. But if you give him some patience, he will open up. He's probably just not used to cute girls starting convos with him.
There's different types of guys some are shy cause of their nature or they like the girl to much, maybe you can ask yourself that question if you like a boy and have a crush on him and you're the one it has to ask him out! probably you will feel scared and nervous