Umm....are you for real?
Pakistan tested Nuclear Weapons in 1998.
The only reason Pakistan started this Kargil incursion was because it had nuclear weapons and it knew that will serve to prevent this localized conflict into a wider war.
Pakistan exploded nuclear devices in 1998, doesnt mean it had a nuclear weapon and a delivery method, heck your F-16's had to be grounded in 1999 for lack of spares. Were you planning to deliver them by Samjhauta express?
And as to why Pakistan did it, maybe you should start asking that question with regards to 48' 65' as well, poor planning and good men left to be massacred thats about all they ever managed to achieve.
That's why you tried to intrude Pak air space by the help of Israel Air force!
India regularly intruded Pakistani airspace before and after 99, they had nothing to stop Indian reconnaissance planes even when a we sonic boomed Islamabad