抛出不适用于布尔表达式的表达式?

抛出表达式在这种情况下有效:

string myStr;

public MyObj( string myStr ) =>
    this.myStr = myStr ?? throw new ArgumentNullException( "myStr" );

但是为什么这个不能编译呢?

bool isRunning;

public void Run() =>
    isRunning = !isRunning || throw new InvalidOperationException( "Already running" );