In proxy wars blame lies on both parties. Insurgencies erupt in those regions where state organs neglected the population and extreme economic depravity exist.You could buy people easily. You would have an idea, what people can do for Money or to keep .Let's say If Pakistan decide to support Maoists or Assam rebels in future, would you blame Pakistan solely ? Correct me, I've read there exist genuine problems and state negligence/exploitation of those areas where maoists are active. Similar grievances that of Balochistan. Pakistan was able to exploit Kashmir issue because local population was and is still anti India and there were genuine problems before insurgency began (Something to do with maqbool bhat and poor economic conditions). Your army heavy handedness exacerbated the problem and made things easy for us.
The point is argument of yours is circular. Blame will travel in circle forever and can't be placed on one party shoulder.
The area on the other side of afghanistan is not plain. There is a reason US army pulled out from Nuristan and Kunar province in 2010. The mountainous region is treacherous. Taking example of turkey and PKK problem. Were they able to finish PKK? No because of the mountainous regions b/w IRAQ and Turkey.
In contrast Punjab is completely plain while Kashmir Border is quite plain hence manageable and you could do hot pursuits in such areas quite easily but not in mountainous regions which require resources that of US ARMY.
If you has time, read this piece of history, Spetznaz tried to do a hot pursuits and failed
Forbidden Vendetta: Spetsnaz strike into Pakistan during soviet Afghan War
And about the airstrikes, We have either Cobra which doesn't have long legs or F-16. To conduct surgical strikes on time, we need drones. who could stay over head for 24 hr, survey the place and strike immediately. While our surveillance assets (C-130, or saab erieye cant hover on afghanistan area for extended period of time) or human intel which should be present on ground in Afghanistan are non existence. So airstrikes are out of question on timely basis because enemy is always on the move in kunar and nuristan.
Then the question comes about resources, Can you think mountainous border can be effectively monitored and secured by a 3rd world country, facing funding issues, running on aid and loan money most of the time ?
Has BSF managed to effectively stop alleged drug flow from Pakistan to India despite being one of the best managed border areas and plain region? Or to that effect has America able to stop Mexican drug cartels supply in to America ? It's mountainous area we are talking about here in AF-PAK region plus 3rd world country cash strapped Pakistan is . There is a reason Iran remains quite frustrated with us on Border situation. because Pakistan has to prioritize at which border region money should go and managing afghanistan border drains away most of the money.
Can you disarm Texans at will ? Texans and Pashtuns are quite similar when it comes to weapons, Both wear it as their jewellery. Isn't Texas most heavily weaponized state of America . Can you disarm groups in texas ? Now moving away from individual level. Let me quote wikipedia here
Najibullah was commie and he would have started proxy wars to get revenge if his government had become stabilized
We chose pashtun card so Afghanistan won't try to instigate proxy wars over durand line. Incase you don't know, from 1950's right up to 70's before rusian invasion, Afghanistan instigated and supported Pashtunistan movement so whole KPK province can become part of afghanistan. they tried to invade Pakistan in 60's. We needed a group who should keep a neutral stance on durand line. Just like You felt compelled to interfere in Sri Lanka so your Tamil nadu state remain unaffected