I wonder why not smallish robots on ground? Something I imagine similar to those we send on Mars and can move on most terrains. They seem easy to build and pro

I wonder why not smallish robots on ground? Something I imagine similar to those we send on Mars and can move on most terrains. They seem easy to build and program (at least naive me means it's way easier than autonomous cars) and can do it without requiring air space which is a huge regulatory issue in most of the world.