A text app where you can't write in devices which usually have physical keyboards (desktop computers)... why do they act surprised that they have lost users?
I feel like a voice in the wilderness but I feel that smartphones were a giant step backwards. There was a movie trailer like this one
https://www.youtube.com/watch?v=ge-x4mPuZ_4
where the minaturization went beyond the desktop all the way to a little phone and it used scenes from more classic movies but the shrinking screen left me with a tragic feeling and the slogan "go big or go home" was left more ambiguous (maybe you would go home).
You might say one great thing about the old Twitter was the ability to have parasocial relationships with brands and if you think that's important you want to put the experience of brand managers first and from that perspective the most important thing is a powerful desktop app aimed at the power user. If you get those users in they could make a site a destination for people, if it's just another way for people to screw around with their phones that's a really crowded field.
If you’re claiming it’s a big step back for productivity, I’d argue that phones and tablets are devices of consumption, few things of worth are produced on a phone or tablet.