Why would a father not want to be on the birth certificate?

I’m 39 weeks and my boyfriend and I have had quite the roughy patch early in my pregnancy but we’re doing better. He told me today that he doesn’t want to sign the birth certificate when the baby is born. That blows my mind. Why would he not? He said he just doesn’t want to. I asked him if he thinks I cheated or something and the baby isn’t his and he says no he doesn’t think that. So I don’t know wtf the deal is but why wouldn’t you want to be on your kids birth certificate? He can’t give me a legitimate answer and I can’t figure it out. I told him if he plans on leaving me then to do it now and if he’s trying to avoid child support, not signing the birth certificate at birth won’t prevent him from having to pay it. I’m really upset over this. Am I overreacting? Wouldn’t you be bothered too?