Its not popular, because it doesn't have firepower at all, its suppression platform primarily, damage one secondarily when upgraded and when unupgraded its regular reinforcement vehicle.
Its not popular, because at the stage of the game when soviets get T3, other factions have their elites and stock infantry decked out in weapon upgrade as well as their own lights that are on field for at least 2 minutes already, inflicting more bleed then soviets can inflict themselves.
It's not popular in what? I see it all the time in team games and I build it a lot myself. Its a great suppression platform and its probably the best AA unit in the game
You don't buy it for killing power, you get it for suppression and AA. AA is progressively more valuable the more players you add since there's more shit flying around
Maybe it doesn't appear in tourneys, but neither do a lot of things that are still popular in team games