This is due to a concept called expense ratios. 

The expense ratio is defined as the annual fee that an investor is charged for the management of the fund. For example, if you’re investing ₹10,000 in a fund with an expense ratio of 1.5%, then you are paying the Mutual fund ₹150 a year to manage your money.

A higher expense ratio leads to a greater deduction in price and a lower NAV. Direct mutual funds, lacking additional distribution expenses, usually have lower expense ratios, resulting in a higher NAV.