Audacity is more of an audio editor though, not a "real" DAW. The most well-known open source DAW I'm aware of is Ardour.
So many random people use Audacity because it's zero cost, and every one of those people is an opportunity to implicitly teach what's actually going.
Yes, they could all go watch Monty's excellent video showing what's going on, but they needn't do that if the tools we give them show everything properly in the first place, they'd just assume "Right I guess it's magic somehow" and only need Monty's video if they needed to actually understand (or argue with people who are wrong on the Internet).
Everything else about Audacity is pitched just right for an audience that doesn't need a full-blown DAW anyway.