Why do some customers ask for credits while their case is in good financial health, have significant cash and their request is not justified?

A one line answer would be "Opportunity Cost of Capital".

If the customer feels his funds can be better utilized and the return on equity will be higher than the interest being charged, then the customer will avail bank finance. 

We do the same things, its just to keep the money longer in the bank and Gain more interest , or to use that money maybe for a different project that requires we pay in full and can land us more profit . It depends on the company