The Mi-8/17 can carry a more useful number of troops that can get in and out much much faster and more easily, yet still carry enough firepower to "suppress" the enemy before or after troops are deployed/picked up.
The Hind on the other hand can not really use its firepower very effectively when coming in and hovering to pick up or deploy troops. It made rather more practical sense for the Hind to shoot and the Hip to pick up or drop off in real combat situations.
For police operations or anti terrorist missions or deploying a small group of special forces the Hind was a good choice, but most of the time the rear cabin contained reserve ammo.