The issue is that some people (appear to be) submitting very preliminary, and arguably low quality work to arXiv to stake a claim to some area. Once that work is "out there", people who were making a more serious effort to do things more carefully are obligated to cite the original work, presumably as part of the related work/background/etc.

I can see how this would be maddening, particularly if you started before the flag-planting paper was even written.