Here's why:

* Lack of vascular tissue: Non-vascular plants, like mosses, liverworts, and hornworts, don't have the specialized tissues (xylem and phloem) that vascular plants use to transport water and nutrients throughout their bodies.

* Water absorption: They absorb water and nutrients directly from their surroundings, primarily through their surfaces.

* Limited height: The lack of vascular tissue limits their size and prevents them from growing tall. They need to stay close to the ground where water is readily available.

* Dependence on moisture: They are highly dependent on moist environments to thrive. They may even dry out and become dormant during periods of drought.

Let me know if you have any more questions!