Why are both ends of the torsion bar identical?

Torsion bars work by being twisted along their length to store and release energy.

Making both ends identical allows the bar to be installed either way without changing its function.

The same shape at both ends ensures even torque transfer and prevents stress concentration at either end.

If you want it super short:

Torsion bar ends are identical so the bar can be installed reversibly and transmit torque evenly from both sides.