They can’t find them, despite looking as hard as they can, because homosexuality is the result of child abuse and pederasty and they don’t want that answer.
Sexual orientation, just like intelligence and quite probably a lot of other traits, likely involve more than one gene. Maybe lots more. Seems to me what thus company is offering is the possible opportunity to lessen the risk of having a child with an unwanted trait or traits. If they suggest anything else, they’re peddling snake oil.
Please note, I am NOT suggesting that, if they can do what they say, this is ethical.