How does the US visa and lawyer system work? (Liz’s denied visa and ghosting layer situation)

Hey. I like to read what happens to know about the situation.

I saw the recent “US visa got denied” stuff. I am not an US citizen.

- How can a visa be denied? With what conditions?

Also:
- Is it a thing in America that a laywer can ghost you after paying them money?

Thanks for replying!