If you're a single SAHM, it's only one of 10 reasons!
You're living with your mom.
You're on PA.
Your baby daddy fronts all your bills.
You're rich because of your rich daddy.
You're a prostitute 2 nights a week.
You're on disability.
You're a trust fund baby.
You're a Celebrity (ETA: Celebrities are rich and can support themselves without PA. This is why Celebrities was listed since many don't understand)
Those are the only ways you could afford to be single and stay home so stop kidding yourself.