Transistors have no registers. They have no arithmetic logical units. They have nothing. They are so simple they can be made up of less than 100 atoms. Transistors have to be connected electrically to other device. Any reverse engineer can trace what it is connected to and it’s behaviour cannot be programmed. If you know that it’s a transistor and you know the inputs, you can know the output. The same cannot be said for a device which runs software, you’d have to additionally know what that software does, which is incredibly more complicated.
Software is ran by microcontrollers. Transistors can be connected to microcontrollers. But they can also be connected to buttons. If there is no microcontroller, there is no software.