Sons of Belial / worthless men
Here’s what it means
The phrase describes thoroughly wicked, lawless, or worthless people.
Why the Bible says it this way
An idiom is a familiar phrase whose meaning comes from the whole expression, not from reading each word by itself.
A helpful detail: In the Old Testament, “Belial” often functions as a word for worthlessness or wickedness. In 2 Corinthians it is used as a name opposed to Christ.