They literally did not.
There is no way around this, but even if you decide to power through with your Olympic level of mental gymnastics into believing that selling code somehow doesn’t circumvent this clause it’s suffice to say that, as you even stated, it’s nothing more than a loophole that clearly defies the original intention. There’s no good reason why Blizzard shouldn’t have closed it by now, which is now coming from a 7 year old post.
They just ignore addons like this, pure and simple. If there’s anything that actually annoys me about this conversation it’s ridiculous statements like these where people try to portray these addon creators as smart people who outwitted Blizzard. Blizzard is some combination of lazy, inept, or have some sort of financial incentive to let them exist as they do. That’s all there is to it.