He's not dating you because he just wants to experiment and seduce for the thrill of it.
He's not dating you because he's emotionally unavailable.
He's not dating you because there are so many other dates going on in his life and the prospect of the addition of his already charged schedule seems like a bummer to him.
He's not dating you because he's dating someone else and Cancerians are mainly loyal partners.
He's not dating you because he wants to stay single and enjoy the benefits.
He's not dating you because he doesn't really like you.
He's not dating you because he knows that's what you want.
He's not dating you because he probably thinks he's not competent enough in bed.
He's not dating you because it's about drowning less in your love zone.
He's not dating you because he's too lazy.
He's not dating you because he's not attracted to you, if you can't wake him up with any of them, try your luck with a less pretentious sign.
He's not dating you because he's bored of dating and he's just out for adventure.