为什么SecurityFactoryInterface #getKey在hypen-separated case中返回字符串？

I failed to find out, where 'simple_preauth' security config parameter comes from, by searching for that string through the project. Later i figured out that actual value is 'simple-preauth'.

 public function getKey()
 {
     return 'simple-preauth';
 }

In authentication factories it returns values like that, but in security config it's

firewalls:
    main:
       simple_preauth:

The case is changed to snake-case in MainConfiguration#addFirewallsSection.

str_replace('-', '_', $factory->getKey())

Why it's made that way?