Not all get refused, it's just a very very low chance he will win. I don't know what you mean by post people do apply, there are a few people here who had former refugee spouses and were successful, but they had to have had a very strong relationship background/evidence.
Let me guess, did your friend propose and marry his then girlfriend, after just a few months from the first meeting? Refugee applicant + quick marriage = almost guaranteed refusal.
Also it depends on the country he's from. Unless he's from a country where there's a good reason to apply as a refugee, such as Iraq, Somalia, Syria, North Korea, etc instead of "so-so" countries like Mexico (a very common one), Pakistan, etc, then his chances of getting deported are high. And when a person gets deported, their chances of being sponsored is almost zero, because they now have a history of being deported and applying as refugee.