They flirt aggressively either because
1. You're taken and therefore "safe" as an outlet because they know you likely won't reciprocate
or
2. That you're married and have a baby on the way is proof that you're good marryin' material. (Although if you left your wife for a hussy what would that say about your likely fidelity to them?
Nobody ever said hussies were good at thinking ahead.)
or
3. You're sexy and they just can't help themselves
