SwingdancerKen: kersh1976: It's a massive shock to the system when you play your first round after reaching the next tier.
I had same reaction.
It may have been a shock for you, not knowing what happened.
But, mathematically speaking, what follows suit is just a massive nonlinearity in the average calculation:
The numbers you have become used to for a while simply disappear. Both average and number of scores are wiped out, reset. In response to the title, it's not increased but it starts over.
After the promotion, you see the display of the last former tier's average with the new tier designation. And then, the first round under more difficult conditions brings a higher score than you are used to, shockingly becoming the new initial average.
Hang on, it will decrease!