Ground wave propagation employ vertically polarized waves around & less than 2MHz.
1] It is less affected by interference.
2] It gets less absorbed and therefore can travel large distance.
3] It is vertically polarized.
1] Due to variations in earth's at-mos. density, polarization can be affected.
2] If polarization changes to horizontal, or has norz component, it gets s/c.
3] As a reason, distance cannot be too large.