The Taliban are not a single entity. There may be a central Quetta Shurah but the majority of "Talibans" are local warlords who find the Taliban cause, power, weapons etc most advantageous at that time. Certain points:
1. The leader of Tribe A through bribery, nepotism etc becomes the local administrator. Tribe B who has a blood feud with Tribe A will have none of this So they try their best to undermine A's authority and will gladly accept Taliban assistance saying A are un-Islamic traitors, American dogs etc. A will in turn will quickly label B as Taliban to get more US/Central gov money and forces to squash their old enemies and to justify their attacks with bonus cred points. This quest for revenge is also the reason that the family of most if not all Afghans killed by American forces (who will gladly pocket the blood money) will gladly kill Americans.
2. The normal Afghan takes their brand of Islam (sodomy, selling drugs is Ok homosexuality, women going without burqa, men with head uncovered, anything labelled Jewish is not Ok etc) quite seriously, at least in public (it being a tribal society the two measures of social standing being honor, basically conformation to tradition, and money). That is why recent measures such as dropping of leaflets perceived to be anti-Islamic and acceptance of Jerusalem as Israeli capital have helped the Taliban cause with even members of the former US ally Northern Alliance joining the Taliban.
3. To the local players Pakistan, Iran, Russia and China US is only a temporary (and disruptive) factor in the region who will have to leave one day so their concern will always be an Afghanistan without US forces. For them the Taliban are a known and relatively more reliable quantity (willing to accept their demands for legitimacy, aid, trade etc) also the one most surely to be the dominant force. This aligns with the interests of the local players (Pakistan-trade, acceptance of Durand Line, curtailing drug smuggling, loss of safe haven for anti-Pakistani elements like Balochs and TTP, etc. China-trade/mining rights, loss of safe havens for Uighurs (and BLA who are threat to CPEC), no future prospect of US being in their backyard, loss of Indian influence in Afghanistan etc). To the Americans pre-invasion Afghanistan was a stone age failed state but to it's neighbors it was calm and ready to do business.
3. Like Pakistan and China Russia is happy with a Islamist Taliban Afghanistan as long as they keep their shit to themselves, reduce drug smuggling etc Although there has been no credible evidence as yet Russia supplying weapons to Taliban makes a lot of sense. Not only it helps to undermine USA (another step in their objective of transition to a multipolar world) but recently acts as a counter to the rise of ISIS which according to them (and according to Hamid Karzai) is being supported by USA. The notion that Taliban and Russia will not talk to each other is wrong as Russia has a history of paying off local warlords and the Afghans are opportunistic as ever.
4. Pakistan most certainly did give Stingers to China for studying but never to Indian terrorists. During the Kargil War they were used by Pakistani irregulars/volunteers read "little green men". No heavy weaponry has ever been supplied to Kashmiris because they are considered unreliable and have inferior fighting qualities as per Pakistan Army's belief in the British martial races theory and experience during operation Gibralator.
Pakistan does not make a copy of Stinger. Their MANPAD Anza is based on HN-5 which is a reverse engineered SA-7. Although the seeker could be based on Stinger's and sourced from China because AFAIK Pakistan cannot produce IR seekers.
5. Regarding unaccounted for helicopter losses:
- The hot and high conditions of Afghanistan are the bane of all helicopters. Helicopter flying in mountain requires years of specialist training and even then sudden local changes can lead to accidents. Helicopter losses of India and Pakistan are indicative of this.
- It is quite absurd that world's most advanced and successful attack helicopter cannot counter old Stingers a system against which they would have been extensively tested. (eg. The recent inability of AIM-9X to shoot down Syrian Su-22 was attributed to the seeker being tested against US flares). Also if there had been such heavy losses India would not have selected the Apache as it would have known about them through its intelligence sources in Afghanistan.
- Russians downplay the effectiveness of Stinger during the Soviet invasion (could be loser's talk). They say after the initial shock Stingers were countered by DIRCM and improved tactics.