UK consumer watchdog Which? has urged Nintendo to "get a grip" on the problem of Joy-Con drift. According to Which?, stick drift is caused by a mechanical fault during the manufacturing process for the controllers, one that Nintendo has apparently failed to correct despite the console being almost six years old.
According to a Which? press release, the watchdog recently sent five Joy-Con sets suffering from stick drift to a teardown lab in order to determine the root cause of the problem. The results found that "likely mechanical issues" were to blame; specifically, dust protection on the interior components of the Joy-Con's analog stick was "insufficient".
All plastic circuit boards within the Joy-Con "exhibited noticeable wear", according to Which?, despite "only being used for months". As such, the lab concluded that wear to these circuit boards, as well as the aforementioned dust issue, leads to Joy-Con stick drift. In essence, the controllers aren't being manufactured with sufficient dust protection, and so dust worms its way into the controller's insides.

Which? specifically points to what it calls "the Classic version of the Nintendo Switch console" in terms of Joy-Con drift reports, but it's easy to find players complaining about this problem across all Switch models, including the newer OLED Switch and the handheld-only Switch Lite. In the latter case, it's arguably a worse problem, because the Joy-Cons aren't detachable like they are with the other Switch models.
This is far from the first time Joy-Con drift has been identified. Nintendo has been hit with class-action lawsuits over the problem more than once; it's been an issue that's plagued the console since its launch back in early 2017. In fact, in September 2020, one gamer actually won a lawsuit against Nintendo over Joy-Con drift in UK small claims court, so Nintendo is well aware of the problem at this stage.
In fairness, it isn't just Nintendo that appears to be at fault here. Xbox has also faced legal action regarding stick drift in its controllers, and in early 2021, a law firm revealed that it was exploring its legal options regarding a potential lawsuit over drift in the PS5's DualSense controller. Even the otherwise-excellent Steam Deck isn't without fault here; it's a recent console, but some users are still reporting drift issues separate from the ones Valve fixed with a firmware update in March this year.

So, what does Which? want from Nintendo? According to the watchdog, it wants Nintendo to provide a "compensation or refund plan" for any UK gamers who can prove they've bought replacement Joy-Cons due to stick drift since 2017. Said scheme needs to be "a 'no-quibble' and completely free of charge repair or replacement" operation, according to Which?.
It remains to be seen how Nintendo will respond to this, although one rather suspects the company will continue as it has until these voices get louder. In the meantime, if you're experiencing Joy-Con drift, your best bet is to contact Nintendo support if your console or controllers are within warranty. If you're a techy type, then you might get some mileage out of the Helder Drift Stick Fix controller mod, although sadly, it doesn't work with Joy-Cons. Stay tuned for more info.