Here's why:

* Mosses are non-vascular plants: This means they lack the specialized tissues (xylem and phloem) that vascular plants use to transport water and nutrients.

* Limited Size: The absence of vascular tissue limits mosses to small sizes. They rely on diffusion to move water and nutrients, which is efficient only over short distances.

* Moist Environments: Mosses thrive in moist environments where water is readily available.

Let me know if you have any other questions!