Why would lender say conventional requires marriage? Must do FHA?

[Sloan Clark]

The clients (who are not married, but live together and are buying the house together) were told they HAVE to do an FHA loan. They wanted a conventional loan, and qualified for a conventional loan from a different lender. But this lender (who is in bed with the realtor) is saying clients can not get a conventional loan, because they are not married.

Could this be legal? I thought ECOA protected people based on marital status?  And the other bank was able to do the conventional loan.

Is it possible that this particular lender can't get PMI/MIP for non-married people? Is that a thing?

Does anyone know a reason why someone would be eligible for FHA, but not conventional due to marital status? If not, what would be motivation for the lender to pressure client into FHA?