Hello Team at US Non-immigrant visas

Im a US citizen..( with dual citizenship ) my spouse is Nigerian. He's been trying to apply for a Non immigrant B1 visa and has been denied 3 times..( once while we were in Nigeria and even now that im in the US to have the baby with my hospice records, invite etc) they still denied without any encouraging hint as to why. Could they be denying him the Visa because im a Citizen? Thats what his family members are telling him and some front door staff at the embassy.. Is there any validity to that?