I think the West is going through an aged period with wear and tear, plus trades of course
Think in the past 5-1- years, the West included primed TimDuncan, TMac, Kobe, Shaq, Yao, Dirk, etc
Now all these players are fading out and newer younger players are taking over, while the East is getting more players, as the OP said.
Boston big 3, Chicago "big 3", Miami big 3
I expect the East to take over the Allstar games for the next 7 years