You said an overwhelming number are rejected, 30% of Nigerians get in that's a one in three chance, a little bit better odds than a lottery don't you think, one in three is not overwhelming at all.Yes, not all of them because as you accepted, the cases are looked at on an individual basis and 30% of Nigerians and 10% of Haitians provided sufficient evidence of being real refugee claimants.
Why people still try even though most get rejected is probably the same reason people continue to play the lottery even though the vast majority of people lose money.