The question is logical one and average interviewer would like to know why you wish to change the line. The problem is not with interviewer per se in asking this question but your inability to give convincing or reasonable reply. What kind of jobs are you applying for? How your teaching background could come handy in execution of the work of that designations? In what stream are you pursuing your MBA? Why you have chosen that stream?
Interviewers might not buy the argument that financial crisis forced you to get into education field. Jobs were abundant for the worthy candidates hence interviewers are taking your argument with pinch of salt. Compared with hustle and bustle of corporate life, teaching profession is considered cushy. The general feeling is that those who wish to have secured life, those who do not wish to be on their toes, get into the education sector. Keeping aside validity of their belief, what you need to consider is existence of this belief.
Not that people do not change their career. Nevertheless, you are bound to meet some amount of resistance and that is what happening with you. Keep on applying and somewhere you will make breakthrough. Early breakthrough will depend on your ability to provide convincing reply.
All the best!