Nail, hammer, head,
IMHO.
Unless a new model either does something new, or something sufficiently better, then expecting users to replace a perfectly functional model with an almost identical new version essentially relies on them wanting to be seen with the latest model. That is, a status-symbol, ego -trip kind of thing.
I think the slump in sales signifies 2 or 3 things.
One - the 'marginal' nature of recent model improvements.
Two - To a point, a growing nationalism in the Chinese market, and the growing sophistication of high-end home-grown products.
Three - a bit more tenuous, but growing nerves about the world economy, the slow-down in Chinese growth and the China-US trade spat .... which also feeds into point two.
Then again, what do I know, or care, as a non-smartphoner.