What so professional nd specific in b.com? 

Muskan, BBA is a general course which will comprise of subjects like basic Economics, Entrepreneurship, Emglish communication, etc. It is not focused on Accountancy, Financial structures like B.Com.
When you're applying for jobs like Accountant, Auditor, etc. They'll require a B.Com degree which specialises in Accountancy and such.

In simpler comparison, it is somewhat like getting a B.Tech degree VS. BCA degree.

Of course there are BBA with specialisations like foreign trade, global marketing, etc. And Delhi University based Bachelor in Management Sciences