SMS is still used in France. It is free, reliable and every phone supports it, making it the default.
I think there are historical reasons. There was a time where most plans had free SMS but expensive internet, and even today the cheapest plans have free SMS and very limited data (ex: 50MB/month for the free.fr 2€/month plan).
Countries that didn't have good SMS infrastructure and advantageous plans are the most likely to have switched to private, internet-based messengers.
I don't know if it is still the case now with 4G/5G and the phasing out of earlier standards, but SMS had the advantage of going through congested networks better than anything else, including phone calls, MMS and internet data. Probably because it is an ouf-of-band signaling protocol.
Those are all closed-loop messaging systems. If anything whatsapp/imessage/whatever are more vulnerable to what was suggested because they aren't open/standardized protocols.
SMS is an insecure protocol from the ground up it was never designed for the mass communications it is now used for.
It is open, sure but it needs a new open standard to completely replace it, which will take decades because its used for machine-to-machine communication in US telecom infrastructure and the sheer amount of physical equipment that would need upgraded is insane.
I think there are historical reasons. There was a time where most plans had free SMS but expensive internet, and even today the cheapest plans have free SMS and very limited data (ex: 50MB/month for the free.fr 2€/month plan).
Countries that didn't have good SMS infrastructure and advantageous plans are the most likely to have switched to private, internet-based messengers.
I don't know if it is still the case now with 4G/5G and the phasing out of earlier standards, but SMS had the advantage of going through congested networks better than anything else, including phone calls, MMS and internet data. Probably because it is an ouf-of-band signaling protocol.