Might be an unpopular opinion but
In the late 2010s or early 2020s, I wrote a short story in the Notes app on a Nokia C3-00. It was one of the budget offerings with a QWERTY keyboard and WiFi support, and it was pretty awesome for the time, and still is to an extent.
By that point I cycled through a few touchscreen phones beginning from tiny Samsung junkers to mid-range Chinese phones we would have called "phablets" a few years back and got used to touchscreens. I'm typing this right now on a touchscreen and it's pretty nice, yeah autocorrect is wrong some of the time but it is solid most of the time, and I can type really fast. Typing on a phone with a small physical keyboard was eye opening in a way. It felt slow, and I had to actually put some effort into pushing the buttons to make them register. In all fairness, it could be the age of the phone making the buttons stiff.
Something else is how the labels on the buttons eventually wear out. If this was a physical keyboard I could just replace it, but a small panel of keys built into a phone? Yeah not really replaceable.
I get that all those very tall, very flat slabs of plastic and metal can get boring very quickly, but I guess because there's not so much more left to perfect that form factor.
I think you might be underestimating how some people type really slowly when given a full sized QWERTY keyboard, numpad and all.
Then again the one limiting factor of phone keyboards (touch or physical) is that they're designed for two thumbs, instead of just whatever fingers happen to be closer to the button you want. Though I'll admit I do miss when Nokia, BlackBerry, etc, came up with unique solutions for how to get a small physical keyboard attached to a phone.