The same should be able to be said about everything on Wikipedia, since Wikipedia is not supposed to have original research and should have a source for everything.
The "Why?" would then be "Because it is better to search for [obscure butterfly] and find a short list of fact than to search for that butterfly and find nothing at all."
A stub also lowers the barrier of entry for new users wanting to add an obscure butterfly they've just tracked down.
I don't think so. Well-written encyclopedic entries are in far shorter supply than bare lists of facts.
I guess the fundamental difference of opinion is between those who feel Wikipedia is an encyclopedia, and those who feel it's a dumping ground for human knowledge. Note that I'm not taking sides, just trying to explain the root causes for the difference of opinion.
Also, on a purely technical note, I very much doubt that you couldn't find the information in bot-generated articles anywhere else using a search engine. If that were the case, where are the bots getting the data?
Or bots could be taking something in a weird set of scans, OCRing that, and then putting it in a stub. This would be troubling unless there was a human checking the quality of the OCR.
There is plenty of stuff that is public domain and not online in a useful form.