Yeah but there are far too many factors here beyond ICC or any governing body's control. There is a lot of gray in this whole chucking issue than most people realize.
1)The officials during the Asia Cup or during Bangaldesh's home series throughout 2015 are not necessarily the same as the officials during the Netherlands game. The action might have been problematic to some, and fine to others.
2) The human bowling action itself is not a constant. It changes. It is quite possible that even if the officials were the same, Taskin's action was fine before, and during that game, he might have done something different, or had a niggle or a host of different factors. So it's possible they didn't have concerns before, but they do now. What do you do about that?
Yes, if someone is reported before the tournament, then we can by all means have them disqualified before the tournament.
The other problem now for Bangladesh is that they have to find 2 replacement bowlers in a very short span of time. This is why I feel that if a bowler has been reported during the tournament, he should be allowed to complete the tournament, simply because of logistical factors. Bangladesh now have to find two replacement bowlers, make visa and travel arrangements, and have them ready before a crucial game within a day or two. And this time, the travel between Bangladesh and India is short. But what if this tournament was taking place in a different continent? What about long flights? Jet lags? This puts the team in an unfairly vulnerable position before a crucial match.