I've always assumed that it's because pigs will eat human excrement. The article kind of, sort of, brushes on that. And that's gross and might be just the thing to push pork from a marginalized, lower class food to outright prohibited.
I.e. when pig farming became a business, people probably started feeding pigs with literal garbage instead of proper animal feed, to make as much profit as possible. Without science and without the equivalents mechanisms of FDA/USDA, inspecting the produced meat for suitability would probably be nearly impossible. This would eventually lead to a series of public health incidents, which would be straightforward to trace to pork.
This would in turn led the clerics to label pork "unclean", in order to protect the public from such outbreaks. This was efficient since it doesn't need rigorous enforcement of the ban, and also would drive down the demand, thus the incentive to feed your pigs crap.
Also, pigs are known to eat humans from time to time.
Yeah... watch a few videos of pretty much any kind of industrial scale meat/fish/poultry farming and you'll shit, blood and piss... which isn't even the most revolting/disgusting things you'd witness
edit: also Sparschwein
even more edit: I grew up in a part of Bonn Bad Godesberg called Schweinheim. Steep hillside up to the plateau of the Kottenforst.
Has been used as so called 'Hütewald' in old times, because it wasn't good for much else, because too steep.
Grunz!
Dogs eat human excrements, but they are totally clean animals. No parasites whatsoever. It is totally safe to keep them in your house and even lick their mouths!
Dogs are totally clean, and they are immune. You must exercise your immune system to get used to it.
The immune system is not a muscle and does not benefit from "exercise" in such a simple fashion. Inoculation is a careful process and does not "exercise" your immune system but rather reliably introduces a new identifiable threat to your immune system's memory. You can inoculate against a million different things and your immune system will be not significantly better equipped to handle a novel infectious agent.
Similarly, you could french kiss every single toddler during flu season and be no better off with a novel pathogen.
You cannot "exercise" the immune system. You can only train it to recognize specific targets.
The Hygiene Hypothesis, the closest thing to a speck of truth that this absurd notion might have come from, is about allergies and tuning the response of your immune system to common foreign bodies.
If the hygiene hypothesis is confirmed or well supported, growing up in a clean room would make your immune system over-active and over-destructive, NOT WEAK.
This stupid concept has grown so much since COVID and it's infuriating. The hygiene hypothesis is super important and is linked to research in human microbiomes and is essential for us to understand so that future generations aren't allergy-ridden hulks, but they would still fight off the flu just the same.
People will believe any bullshit just so they can continue to think getting a damn vaccine was somehow not the right move!
If you want a healthy immune system, then eat well, sleep plenty, get your fluids, and get vaccinated!. If you die from a preventable, communicable illness, your immune system won't be able to protect you from decomposing
/end rant