Visitor Visa - B2

Good day, I just found this website would be of helpful to me in knowledge and advice in getting a business/conference meeting visa.

I had been rejected twice for the business / conference meeting visa and I would like to know what I was doing wrongly because I'm planning to reapply again.

First interview was done in Malaysia when I was doing my MBA program in Management and research also for the Uni due to insufficient needed documents.

Second interview was done back home in Nigeria and I was rejected again. Here below was how the interview conducted.

VO- Good Morning
Me- Good Morning
VO- Why are you going to the US?
Me- For a business conference
VO- What kind of work do you do?
Me- A business development
VO- What is the name of the company?
Me- Answered
V0- Have you traveled out of the country before?
Me- Yes
VO- What purpose?
Me- Studies
VO- What is your highest qualification?
Me- MBA
VO- Have you attend any business conference before?
Me: No

He typed something on the computer and said We are sorry but your visa is rejected this time. You can reapply again.

No document checked. Can someone please tell me the missing point or knowledge gap because I'm planning to reapply again in a week time. Could it be because I had been rejected once in 2010? This upcoming conference is important for my new career, team members and also for the organization I worked with.

Thanks