Why doesn't the generated PV power follow average available energy, when moving from the Equator to the North Pole?

Great question.  The "average daily radiation" is actually the "average daily radiation on the horizontal surface".  The output of the PV array depends on the radiation striking the PV panel, not the radiation striking a horizontal surface.

Here's the key thing:  At the pole, when you point the PV panel straight towards the sun (which is what happens with two-axis tracking) you get a lot more radiation than when the PV array is horizontal.  That's because the sun is always low on the horizon.  At the equator, when you point the PV panel straight towards the sun, you get a little bit more radiation than when the PV array is horizontal.  That's because the sun is often high in the sky.

That explains why the difference in PV array output between the two locations is smaller than you might expect.