IN is sanctioned to operate 15 destroyers and 24 frigates. But IN has no actual need for that many smaller sized frigates, hence the P-17 and 17A are actually destroyer-equivalent. But with the frigate designation, IN can place more orders for it compared to destroyers.
The only reason we ordered Talwar class from Russia is because we urgently needed ships back in the late 90s. Since the ship was pretty good, and demand was greater than supply, follow on orders of the Talwar class have continued.