Why do bryophytes and ferns depend on free water to complete their life cycle?

Bryophytes and ferns need water as the medium to complete their life cycle. The male sex cell of both is flagellated and hence motile. These flagellated male cells combine with the female cells to fertilize.

However, for the process of fertilization, the male cell has to swim and reach the female sex organ. Both bryophytes and ferns require a moist surrounding in order to reproduce.