The SIL Open Font License is pretty much the standard for freely releasing fonts. Poke around on Google Fonts or other places that have freely-licensed fonts and you'll find the vast majority use OFL.

Adobe's Source (the basis for this one), Google's Roboto and Google Sans, the very common Inter, Lato and Open Sans, coding/monospace fonts like Iosevka, JetBrains Mono... chances are that a free font you're aware of uses the OFL, particularly if it's even vaguely recent.

I don't believe they had a choice, since it's a derivative of Adobe's OTF-licensed Source Sans.