查查词典就知道了，the powers that be 是习语，指组织、国家等的“当权者”“当权派”。如：

The powers that be don’t want the media to get hold of the story. 当权者不希望媒体知道那件事。

It’s up to the powers that be to decide what should be done next. 由当权派来决定下一步该怎么办。

The powers that be may keep us from building a house just where we want to. 当权者可能会阻止我们随意建房屋。

你的句子意思是：

It’s the powers that be who decide things. We just have to live with their decisions. 当权者才有权力作决定，我们只能接受他们的决定。