I guess because Whatsapp provides a unified and standard way to communicate between people on different provider networks / countries for free? You get groups, text/images/location sharing, video/audio calls, cross-countries, that works very reliably, and you only need internet (which can be found almost anywhere even if that's just wifi).

MMS still don't work reliably for me (lost a message just last week that someone swear to have sent). And for a long time they were not free as well.

This is still where normal phones work better (no internet).

I'm not actually suggesting using MMS. I just wanted to illustrate that we've had instant communication technology (even "rich" multi-media) long before Whatsapp etc. Why didn't the providers of that technology (telecom companies) become Meta?

The difference is that MMS/SMS is standardized and agnostic to the client interface. While WhatsApp is proprietary and monopolizes the client.

We could easily have had a "internet direct message" standard implementing most of WhatsApps features. (Wait... Isn't that SMTP?)

Maybe I'm just ignorant, but what does WhatsApp bring that let's say email++ does not have?

Telcos hire vendors to run their networks and services. For them WhatsApp is yet another vendor.

It was a great and useful cross platform messaging app ... and still is after Meta bought it.

MMS has been exorbitantly, insanely expensive and with extremely high failure rates in much of the world until...

... actually that's still the case in varying degrees and locations. And once you've got great market penetration in an area, there's little to no reason to switch unless the competition is noticeably better, which MMS really has no claim to.

Point is: why did an open standard for direct messages not win over proprietary solutions?

They put in quite a lot of time and money to build it and make it work on a ridiculous array of devices running weird embedded OSes.

Open standards hadn't.

Or if you're referring to MMS: insane user cost and insane unreliability, standards mean nothing if the implementations are all trash.

But why didn't email win over WhatsApp? Doesn't email run on all devices?

Not saying it should have, just that I don't really see the difference in functionality.

Email definitely did not. When WhatsApp was beginning its rise to domination, it was on tons of feature phones - mostly just calls, texts, and WhatsApp. Email implies a lot more general internet access than was generally supported or understood by people, since it supports arbitrary data and hosts.