Bangladesh never really developed a smart but aggressive batsmen. Brad Hodge is a good example. He is a smart cricketer and can find boundaries. In t20 the Bangladeshi's mindset is to just hit the ball and hopefully it goes to the boundaries.
It might for a short time but for the long run it will be no chance. Thats why we see players like Ashraful, Aftab, Siddique, Raqibul etc flop.