No one will invest even after Android is closed.

The Android/iPhone duopoly is nearly impossible to break because very few people want to carry two personal phones, and it takes only one app that they can't do without being only available on Android/iPhone to make it impossible to choose anything else. The app providers likewise have no incentive to support anything else because everyone has one of these two.

Bank apps are the prime example here that's unlikely to start supporting other systems. Public transit (and in some places parking) is another potential problem where even the unhinged "well just change banks to the one that does support your favorite phone" argument fails. ID apps (either governmental or de facto standards like the Swedish BankID) are coming too.