Android has more market share but iOS has the users that are most profitable. They're dominant in affluent countries (USA, UK, plenty of countries in Europe, etc) and even in countries where it isn't dominant, it's not rare for iPhones to be the phone of choice amongst the wealthy population.
Wealthier people, I imagine, are not only more likely to want to buy things, they'll also be more willing to spend their money on new things.
To get a sense on how much more valuable "valuable" consumers can be for Facebook: last quarter on average they made $60.57 dollars per user in the USA/Canada, vs just $4.89 for their users in Asia-Pacific, for example [1]. The USA and Canada are still Facebook's biggest money-making region, in spite of also being the one where they have the fewest active users [1].
I'm not sure if an immediate 25% share price dip makes sense either, given worldwide Facebook lost only 1 million DAUs, and the number of users in the USA/Canada has steadily oscillated between 195/196 million since 2020 (the loss was in "Rest of the World" the catch-all region they make the least money in.
A lot of the value of these companies is not necessarily realized value, but value derived from the expectation of continued growth at a certain pace.I can see why investors are nervous; Facebook has never lost DAUs, there's intense competition with TikTok for the young demographic, VR/AR has been a huge bet that still hasn't paid off and the controversy around Facebook weakens the value of the brand. On top of this, in spite of revenue being good, it was not what was expected and effectively advertising on the valuable iOS demographic got much harder. Maybe that warrants a 25% dip, maybe it doesn't— in any case there's definitely reasons to be nervous.
[1]: https://s21.q4cdn.com/399680738/files/doc_financials/2021/q4...