I imagine the Japanese are more patient so they stick with the same group till they learn each other strengths and weaknesses while we are impatient and will shuffle members in and out of a static like MtG cards till we find the "I Win" deck.

And then a new raid starts and the "I Win" deck doesn't work...so back to shuffling cards in and out till the new "I Win" deck is formed.

I also don't raid or anything so I could be WAAAAAAAAAAAAAAAYYYYYYYYYYYY off base till the point my theory is stupid.

*shrug*