The West Indies and Sri Lanka team right now might not have players who are molded in the T20 format and so is the reason we are not seeing any aggressive game play.
The cricket board will not mold any players to become aggressive. I think they have the perfect batting line up for Test matches and i am impressed with they way Sri Lanka played in the last two matches and somehow managed to draw the match and both these teams are experimenting with new players and give them some time and we might see good players emerging from these countries as we have seen some good defensive batting from some of the players in both teams.