Why do a Science grad.(mathematics) do MBA?

Become a member of senior management in the company.

Just some reasons that I can think of right now. There may be more from other folks, though.

1) You will have more education which better prepares you for the job market and to serve people.

2) A lot of jobs that you will apply for require you to have your Masters in Business
Administration. Very much like so many colleges and universities will not hire
Someone unless they have, at least, their Masters Degree. And, oftentimes, nothing
Less than a PhD.

3) Having a Masters Degree can mean more pay because whoever hires you may have a
Salary scale based upon the amount of schooling that someone has.

4) If you are looking to start your own business, then having an MBA may make you look
Better to potential customers.