When you lease an apartment, do you get the details via WhatsApp/WeChat/TodaysChatApp or email? How about receipts, bank statements, anything where deliverability actually matters?

Email is infrastructure; people invest in it. If the only people investing in these chat apps are themselves people, these apps could be ghost towns in years.

In some sense you're right; in another sense, it still seems like email is likely to outlive walled gardens because there's no long-term reason to use them.

In particular, unless there's a decent way to ensure that nobody can take my received messages away from me, i'm unlikely to adopt it for anything but chatting with friends.