It's neither persistence nor stubbornness, it's just the slow realization in South Block that no meaningful negotiation is possible under the current circumstances. For one, Nawaz Sharrif has no political capital to invest in any negotiation on any topic at all with India. Two, by invoking again and again the UN resolutions Pakistan has left no space for India to engage in any form of meaningful dialogue; India is not going to be party to any negotiation where the starting point is Indian withdrawal from Kashmir.
On what basis do you claim that Kashmir as an issue is independent of terrorism? Mumbai 2006, Kabul 2008, Mumbai again 2008 showed that the very elements that fight in Kashmir against us attacked and slaughtered Indians well outside Kashmir. The fact is, Kashmir is inseparably intertwined with terrorism and presents a credible threat to us.
Further, conflating the official narrative GOP (we exercise no control over the Kashmiri mujahideen) and the comments by the leaders of the terror organizations (We will not stop at Kashmir, we will conquer India/Delhi), there is no reason for GOI to believe that resolution of Kashmir even in favour of Pakistan would reduce our primary concern i.e. terrorism emanating from Pak soil. On the contrary, given the psychology of human nature, there is every reason to believe that these terror groups would be emboldened and launch their version of Jihad on a massive scale. This coupled with the fact that terror emanating from Pak soil will still hold the possibility and risk of a war in the subcontinent removes any merit for India accepting a resolution on Kashmir at any moment in the near future. Status quo presents the best and most logical position for India.