Replit’s mobile UI is not designed to be used horizontally. It would add a bigger width, but the code and output are mostly displayed vertically, so you would limit your ability to see large project files and outputs from your project.
The app isn’t really designed for that. It’s designed for on-the-go coding, or just fixing a bit of text real quick on vacation or something (in most cases). So you usually wouldn’t need to rotate to the bigger screen and get out your whole keyboard and mouse and stuff.