Why do certain guys flirt with every girl he sees?
he is cocky
Well I'm sure if you asked them that, they would either deny it or say something along the lines of "I'm just examining all of my options"
There is nothing wrong with a little flirting. If he overly flirts then he is just trying to feel better about himself. He is masking his low self esteem by putting the focus on the person he is flirting with.