What is going on with all of these iFixit batteries being duds?

IMHO…

I have noticed this trend ever since the Throttling issue came out about a year ago and Apple’s offer to replace batteries for free or at a low cost. These issues have caused people to take note of their battery performance and many are eager to replace otherwise good batteries so that they have “perfect” batteries.

I suspect that with this excessive demand, lower quality batteries are making their way through the supply chain where they otherwise wouldn't. Even though iFixit does a lot of QC, I doubt they check every battery (please correct me if I’m wrong!). I would expect things to normalize starting next year when Apple no longer offers the cheap replacements.