The root of the problem lies in the conventions of academic research. Family history research is just that, although many enthusiasts are unaware of it, and have never brushed up against the "rules" which govern it. Researchers are expected to review what has been published previously, present their own findings and draw conclusions, then include a list of sources. The sources should include primary sources, which family history is generally good at, and also secondary sources - i.e. other people's work in the field, which Ancestry never explains, and has allowed it to become a free-for-all.
In the academic world you would not get far by behaving like this, and most people expect better manners, but there are those who do not understand it and Ancestry does nothing to educate them, so this is the result.