I feel you're just trying to find any reason to dislike a phone keyboard.

This one hides away, so the "takes valuable screen real estate away" angle is not valid.

So instead, beware of dust!

Anyhow, have no idea why they would be dust traps. People's cases are far worse for that.

(I don't use a case)

I'm pretty hard on phones - I tend to end up having to pick all the dirt and sawdust out of my charging and headphone ports a couple of times a year. But somehow I don't remember having issues with dust in keyboards. I think on a lot of them the keys were all one piece of flexible plastic so there wasn't really a way in.

Not in my experience. Maybe some pocket lint makes it between the keyboard and the screen, but that's easily wiped off. I don't live near a desert, though.

I had a couple of HTC PocketPCs and a Palm Pre back in the day. All were sliders and never had dust issues. Just unpolished UI (WinMo) and underpowered hardware (Pre).

I'd love a "modern" phone that's a slab with a landscape slider keyboard. Don't care if it makes the phone thicker (especially if they use the space to cram in some more battery capacity).

My sliding keyboard phone used to disassemble itself whenever I dropped it, which had the unintended benefit of being self-cleaning.

Foldable phones, canceled?