The problem I've been seeing lately isn't a lack of spark plugs but a lack of genuine spark plugs. The entire supply chain, including the dealer network has been infiltrated with Chinese fakes.
I've been bit twice now by fake Motorcraft plugs bought right through the dealer, who either has been buying cheap Chinese fakes or the whole sale supplier they've been using were doing so. I've seen the same with all brands.
A neighbor bought plugs for his Stihl chainsaws, (he's a tree trimmer). One of the plugs fell apart ruining an $800 saw. It turned out that the Bosch plug he bought several boxes of from reputable online source were counterfeits.
I use NGK BPR6ES plugs in my mower, I've had four bad new plugs so far this year. I avoided buying them from online for cheap because I couldn't see how someone could sell a plug that sells for $6 each at the dealer can be only $1.42 each online with free shipping.
The mower has always killed plugs, I would get a year, maybe a bit longer out of a new plug, but the new plugs I bought back in January from the big box store, were all bad, they wouldn't even start for some reason, despite having visible spark out of the motor.
Yet the $6 plug from the dealer runs fine.
The dealer, and several emails to both NGK and Honda both told me that they've had issues with counterfeit plugs. The dealer told me that he had to return four cases of plugs last fall that he got from Honda which were all fake, meaning that they have somehow infiltrated the OEM parts supply as well.
The double platinum plugs in my car cost $17 each at the dealer, the coils are $81 each. I can buy the set of 8 coils and 8 plugs with free shipping on Amazon or Fleabay for less than $30.
The problem goes even deeper into other items as well.
While this is sort of unrelated here, back during the pandemic, when basics like TP was hard to come by, having lived near the plant where it was made, I called someone who knew what was up to try and score a supply. I was told that they had shut down the plant and were producing no TP there until further notice. At the same time there were unlimited supplies of their brand on Amazon for cheap, shipped from China. Now, four years later, the brands' own website directs buyers to Amazon who only pushes the Chinese sources.
When I called and asked if they were making TP in China, I was told a firm no and they didn't know how that was happening because they don't ship product to China nor do they drop ship or sell any product cheap enough even at the wholesale level for anyone to be selling their brand at that price. But yet their own website directs people to a source of only that supposedly counterfeit product.
Out of curiosity, I ordered a pack of it, waited for two months before it arrived and what I got was not at all the same as what I buy in the stores here. When I called the manufacturer to find out why the link they have on their site sends people to a Chinese seller on Amazon who obviously is shipping counterfeit product, I got put on infinite hold that lasted until they closed. Further calls were ignored. I see the brand getting a ton of bad reviews on Amazon by people who also bought the cheap TP and got something that was completely useless.
Now I'm seeing the Chinese version of it in Walmart too for full price.
I think we have the same thing going on with spark plugs and other items. If the manufacturer wasn't somehow in on it, they'd likely flat out call out the counterfeit sources and take down the links to places selling them unless they all fear that if they admit there's so many counterfeit product out here it may crash their business completely.