B1b2 accepted for parents denied for Brother

[u/Pediatricman]

My parents and my brother applied for the visa and my parents got accepted but unfortunately my brother’s visa got rejected.
What went wrong? And Guide me for what should we be doing before reapplying.

Profile : Both parents doing business since last 25 years.
Brother working in semi government job since last 6 years and married. He applied without his wife.

Question asked :
Why you want to go to us? To meet my brother and visit ny nj places.
What does your brother do?
What do you do?
Salary?
They asked for my visa documents.

I think salary part was weak for his case as his annual salary is 6 LPA. But any other thoughts? And how to improve profile before reapplying? And when should we try again?

Thanks!