to not be expected to explain or provide a reason to a particular person or organization for your actions

The military and CIA hire contractors who are completely unaccountable to Congress. 军方和中央情报局雇佣承包商，这些人的行为完全不必对国会负责。

an unaccountable and inefficient bureacracy 不负责且效率低下的官僚体系

not able to be explained or understood

For some unaccountable reason, he keeps his wallet in his underwear drawer. 不知何故，他把钱包放在内衣抽屉里。