Data is considered stolen when it's duplicated without consent. Hence, "made publicly accessible" is incorrect. It was never "public"...people browsing the web couldn't have stumbled upon it, any more than people riding a train could accidentally have wound up on the moon.
The moon thing is a great analogy. Everyone knows the moon is there, but the process of getting to it is an enormous task beyond the reach of all but the most determined, skilled, and well-financed parties.
It was stolen, not made "publicly accessible". You or I could never have accessed it, it took a sophisticated team months to do it.
Don't forget the Yahoo! and Marriott breaches, both of which were considerably larger than the data "Equifax made [...] publicly accessible".