The best part is that the immigration officer assigned to your "case" can repeatedly ask for additional evidence (called RFE - request for evidence), and ultimately reject it for the most ridiculously superficial reasons.

The way my lawyer explained it to me made perfect sense: USCIS's job is to reject visa applicants, not to accept them. The more visas they reject, the better they look in the eyes of an electorate who by and large hates foreigners "stealing" jobs from Americans.