India wants Pakistan to completely dismantle the Kashmiri Freedom movement and support for it. Either that or it wants to isolate and sanction Pakistan internationally by linking the Kashmiri freedom movement to terrorism.
That is why India isn't sharing evidence on Mumbai specifically. Because if India shared evidence and cooperated, Pakistan would most likely charge Saeed and Lakhvi in court, and if the evidence was strong, they would get convicted. But when that happens, all pressure is off Pakistan because she will have 'acted against terrorism' and 'brought the Mumbai perpetrators to task'.
India doesn't want that - she wants to use this opportunity to mount pressure on Pakistan to dismantle the entire Kashmiri movement, like I said above. The longer the Mumbai perpetrators remain unpunished, the longer India can attempt to sustain pressure on Pakistan, and try and tie the entire Kashmiri movement to terrorism. If the yardstick for 'cooperation' becomes action against the Kashmiri movement, instead of action against the LeT, JuD Lakhvi or Saeed, then Pakistan can really be pressured and isolated.
The Mumbai attacks have become a pawn in this game.