Because the A-Series round of financiers think that's a great idea.

The real answer is because you want all your conversations to happen in the same app/protocol. You never have to download a shiny new messenger again

I'ved heard that pitch before. It's always true only for some length of time. Protocols change, services evolve, companies transform, products are deprecated and people are fickle.

I've used all-in-one messengers before. They come and go like the wind. You'll be downloading a shiny new all-in-one messenger periodically anyway.

Just trading one kind of inconvenience for another.

Perhaps if we normalized messenger interoperabiltiy, there would be less churn in "all-in-one" clients. That churn exists mostly because platforms actively fight their users on this.

And still, periodically changing an all-in-one messenger is still better than keeping and changing half a dozen messengers.

Unless those official clients have features not available in the all-in-one client. Like encryption, which this one apparently lacks.

The benefit of an all-in-one client is that they can port/shim/polyfill[0] missing features between the backing platforms.

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[0] - Whatever is the most appropriate webdev word of the day.

And the downside of an all-in-one client is that they are going to have to port/shim/polyfill features from a hostile, proprietary, changing API.

Once again, the problem is not technical, it's political. Until interoperability is enforced by government, I expect companies to keep building their siloes. Network effect and tragic commons and all that.