Islamic scholar defined that any alms can be directly paid to the needy (which also been clearly defined). But in my country ruling, all the benefit of alms donation (tax exemption, etc) is applicable only when the alms is donated to specific government agency.

IMagine the huge sum of money which is different pool than tax money.

Large pool of money will attract attention and political pressure from dishonest individual in power.

And, when the agency is only focusing its effort in collecting the alms instead of distributing it to the needy, then the pool will only get bigger, and be the source of tension within society rather than 'peace of mind' force.

so far there is no 'huge' scandal erupt yet. The key terms here is 'yet'.