I think it has to do with the messagin app. For some reason in the us it's still common to use plain sms messages, which on an iPhone get translated to the blue bubble, but when sent to an android become the infamous green bubble.

This is however not the case in the EU bc sms messages were still expensive enoughfuring that time that when whatsapp released, everyone did the switch so as to not to pay the sms fees, and now, even if sms are basically free, everyone uses whatsapp as the default messaging app.

And as we know on whatsapp there's no differentiation of anything regarding the device you are sending messages to, so no constant reminder of "this guy had an android".

Just my 2 cents on why this could be.

While other commenters are correct about the marketing in some aspects. As a parent of teenagers I will say if they don't have an iPhone they will be mocked relentlessly. The whole bubble color thing is real. They think androids are for poor people even though androids have a much larger range of price. This isn't a "my kids" thing. This is a "everyone in school thinks" thing.

God help me when they get their next upgrade and suddenly my chargers start going missing because "someone stole" theirs...

Apple is headquartered in America and used a lot of marketing with celebrities, musicians, trendsetters etc.

Samsung is really popular in Asia. There's something to be said for homefield advantage.

What's the carrier situation like in the EU? Do they market the iPhone aggressively in Europe? I'd suspect both of those may have some influence on the difference, but I'm as interested as you in what's affecting the differences in adoption between both regions.