Since no weather is shown, I’m assuming the hold is for traffic. Is the initial west bound track after departure for killing time also?
That’s a normal approach track to ORD for traffic from the South and East.
I don’t know what that initial west track out of BNA was.
It looks like it was originally going to head west over Memphis, then Little Rock, and then approach Chicago from the Southwest. Then, once they were airborne and headed west, they requested, or got assigned the more normal route over Marion, Indiana and on the arrival route from the southeast into Chicago.