Why here Subjuntivo used in the song Hijo de la Luna?

Question

In the Spanish song Hijo de la Luna, at the beginning:

tonto el que no entienda

cuenta una leyenda

que una hembra gitana

conjuró a la luna hasta el amanecer

I think, the "entienda" is in subjunctive form, but why? Why not in present form?

Thanks in advance.

Answer 1

el que no entienda

It doesn't refer to any specific person who doesn't understand something but, rather to some hypothetical person who may not understand whatever (an unspecified topic).

Answer 2

It is a poem,you know, so the poet is taking some liberties here.