That's not just the US. I've seen that myself with Vietnam and Seychelles, and I'm sure it's a problem with any other country where a visa or other documents are required

Last time i had to get a visa through these kind of channels, it looked almost deliberate. Outright bribing is now frowned upon, so they make the visa process as frustrating and opaque as possible. So that people have to either waste several days at the embassy, or go through one of those visa agencies instead. You pay for a totally legit above-the-table service, but it is effectively a "socially accepted bribe". And the administrative problem magically disappears.