I presume no-one has gotten around to fix it yet. Maybe they didn't have any screenshot that was a good representation when they put up the mobile warning. It's not going to happen magically by itself so feel free to send a PR:
https://github.com/tobspr/shapez.io/blob/5a3807883e44640bb8a...
My point is that this is an open source effort. It's not like someone intentionally omitted a screenshot to annoy people. It needs a contributor who cares about changing the mobile prompt for it to be fixed.
I have a similar useless prompt in one of my open source games and it's just a boring issue to fix and I rather focus on the game itself.
The “what a complete crap” belongs only to the shapez.io (mobile) home page. I just can’t believe that it was designed this way.