"From the time the Beit HaMikdash was destroyed, prophecy was taken away from prophets and handed over to fools" (Gemara, Bava Batra 12b).

The Shechina (Divine Presence) only dwells on a joyful person, and after the destruction (of the Beit HaMikdash) joy has been abolished from the hearts of the intelligent. Fools and children, however, can be joyful because they lack intelligence" (Maharsha).

"Sometimes Higher power dwells on them" (Ein Yaakov)

"This can be compared to a king who arranged a large meal [but before their partaking in it] his servants sinned to him. [Seeing this,] the king commanded to throw the whole meal to the dogs. The same is true about the gift of prophecy. Since Yisrael sinned, Hashem disgraces them by giving this gift to those lacking intelligence" (Torat Chaim)

"Prophecy was given to fools since by them the screen
 (i.e., the brain) is not so strong.
The brains of fools are damaged, and one can peek within the world of the soul without any physical concealment or cover.

When the brain is damaged, the soul is freed. It is unlimited and sees all. The brain is what limits and conceals the soul"
(HaRav E.E. Dessler, IV)

"...before disaster and destruction happens to some nation,
Heaven announces this throughout the whole world . . .
and sometimes this is transmitted to fools who lack intelligence"
 (Zohar)