Question

what are the reason why banks are not willing to lend to certain borrowers

Answer 1

Banks might not be willing to lend to people who

have no collateral
have no salary slips or tax returns
cannot furnish documents of employment
have no person to stand as surety
do business which involves high risk
have a history of non-repayment of loan
In such cases, banks do not have a guarantee as to whether or not the loans will be repaid by the persons concerned. It has to be understood that banks only mediate between those who have surplus money and those who need money. Banks in fact borrow the money deposited with them, and lend it out to persons requiring money. They would thus be unwilling to advance the money to individuals from whom repayment is uncertain.
hope it will help

Answer 2

there are many reasons for it.
May be there is less possibilty of the return.
not having proper documnt is also possible.