Apple lost it by getting boxed into a market share corner by android. Google lost it by losing control over android. Android OEM's lost it by getting stuck in a cutthroat competition. Microsoft lost it by being microsoft. Users lost it by having no good choices left (either go with the golden cage iphone, or go with the privacy and security mess android).
Now OEM have to obey to Google because losing the Google apps and services licence (thus losing the Play store and the whole ecosystem) basically means they're dead as an Android manufacturer.
That works in China because Google is relatively weak there. It also works for Amazon, which has its own store for Fire products.
Apple was never likely to license iOS to other manufacturers, nor were they likely to have enough capacity to satisfy the whole market. I reckon they are where they always wanted to be: owning a very profitable and locked-in niche.
You mean the corner where they are the premium smartphone vendor, taking 90% share of global profits? That's a great corner to be boxed into :)
Because iOS users are a significant source of potential profit.
Apple doesn't need to maximize usage in order to control the ecosystem - they just need to maximize profit potential.