Why does wp_remote_fopen return false?

I am getting false when I try to

$json = wp_remote_fopen( dirname(__FILE__). '/webfonts.json' );.

On the other hand, I am getting correct results when I try to

$json = file_get_contents( dirname(__FILE__). '/webfonts.json' );

Do you know why?

(side note: var_dump(ini_get('allow_url_fopen')) prints 1)