It's not "richer countries", unless none exist in Europe or Asia. SMS has only kept its primacy for text communication in North America. Also note the RoW has never had to pay to receive SMS.

But NB even where messaging apps are defacto norms, most of the confirmation and verification for businesses remains via SMS.

Europe is in a weird middle-ground where WhatsApp is still dominant for person-to-person messaging. Not only was SMS costly back when WhatsApp emerged, users are also split 50/50 between Apple and Android, and SMS between them wasn't nearly as good as Whatsapp for the longest time. But WhatsApp Business is not a big thing. Of course that's vastly overgeneralizing, local differences exist, Europe is a big continent. But I mostly see SMS for transactional messages, and platforms like Instagram DMs for actual two-way communication

Interestingly enough, Instagram has none of this weird pricing stuff on their messaging API, despite being run by the same overlords

Fair points, the geography/margin angle is real. Two bits of nuance:

In a lot of those "poorer" markets WhatsApp isn't cheap-SMS, it's the actual commerce channel. People browse, ask and pay through it (India, Brazil, Indonesia, MENA), so even on thin per-message margins the volume and conversion are way higher than email/SMS ever hit there.

In richer markets it's still dominant for messaging across most of Europe and LatAm, RCS is still fragmented (Apple only just added it, carrier support is uneven), and email open rates are a fraction of WhatsApp's. So I'd push back a bit on "everyone settles on email/SMS."