Who can help me explain why the running capacitor of this single-phase asynchronous three-wire motor should be connected to the two wires with the largest resistance?

If someone else contacted this, it may be wrong. If the main winding is used as the secondary winding, the secondary winding is the main winding. Of course, the motor can also rotate, but the direction of rotation is reversed and the force is small.

You can look at its steering and see if the rotor of the motor is strong. If the force is small, it means that it is reversed.

The following figure shows your current connection.