A keyboard is not just to enter text It can do a multitude of things like emojis. Good luck remembering all the mappings on a physical one, or you end up with having them eat screen space. Might not be your use case, but a vast majority of the world uses it.
Additionally, this increases the overall screen real estate. Aside for sliding keyboards (which I did add a caveat for in my original comment), a physical keyboard would be in the way for most of the usage an average person makes on the phone, like watching videos, looking at pictures.
A physical keyboard would probably weight more as well (this is just a guess, based on the idea the membrane, and additional circuitry required for a keyboard would be more than the weight of a glass panel).
A physical keyboard adds an additional point of failure on your device as well.
I'm not saying virtual keyboards are perfect. Like any other thing, there are trade offs to make. But in the form factor phones work in, a virtual keyboard makes more sense according to me. The best of both worlds would probably be a sliding keyboard, but that does add more weight to the device.