It seems reasonable to disagree about whether companies should have the right to prevent forks based on their public data sets ("can you fork the phone book?"). It does not seem reasonable to suggest that Craigslist sued simply in order to be tyrannical.
[1] - https://en.wikipedia.org/wiki/Feist_Publications,_Inc.,_v._R....
Or, for that matter, because somebody was using up their bandwidth, which is a finite resource, for something other than the intended purpose of the site.
To focus on the act of scraping itself, consider a case where they download the data and study it privately. That should not go to court, even if they broke the ToS, unless there are measurable damages.
edited: this said "for 3taps" before, but I'm not sure that's accurate.
I like your analogy of the site being forked. I don't believe for a 2nd that the companies scraping the CL data and putting a pretty UX on it were doing it out of any sense of altruism.