Why are people who say "There is no God" called fools?

The fool has said in his heart, “There is no God.” They are corrupt, They have done abominable works, There is none who does good.

Psalms 14:1 

What is the significance of calling atheists fools? 

Is there no evidence for the existence of God? 

Resources: 

http://96tolife.blogspot.com/search/label/Atheism?m=1

https://www.livinggodministries.net/living_god_ministries/radio_archive/audio_files/romans_13_existence_of_god_1_18_20.mp3