[mdaniel]

I would expect it's roughly the same answers, just varying in the specifics:

* those which don't offer a _reasonable_ API, or (I would guess a larger subset) those which don't expose all the same information over their API

* those things which one wishes to preserve (yes, I'm aware that submitting them to the Internet Archive might achieve that goal)

* and then the subset of projects where it's just a fun challenge or the ubiquitous $other

As an example answer to your question, some sites are even offering bounties for scraped data, so one could scratch a technical itch and help data science at the same time:

https://www.dolthub.com/repositories/pdap/datasets/bounties