In the same way that turning up the volume helps people who are hard of hearing to hear. Colorblindness is a spectrum, not a switch; many people who suffer from it simply have reduced sensitivity to a color. I'm mildly colorblind myself; I can see green, but I can't see it as well as you can.

Upvoted because this is a legitimate question.

I'm slightly grey-green colorblind, and if you make text standard CSS green (#008000) I sometimes have trouble telling that it's actually green and not dark grey. If you make it just a little more green (say #00A000) it's much easier for me to see.

That's not how colorblindness works. Green things aren't invisible to colorblind people. They just can't discriminate some colors from others as well. I would guess that this color is more different from the body text in some color channel that's extra useful for contrast for colorblind people.