Mutual Fund Companies pay out dividends into your bank accounts only if the dividend amount is more a certain minimum (generally ₹500-₹1,000, but differs for each AMC) decided by them.
There are situations where the dividend payout is less than this minimum amount set by them. As processing payouts of small amounts is not cost effective for the Mutual Fund Company, they will compulsorily reinvest your dividend into the same scheme.