> You had to buy them on AliExpress rather than your local Apple shop but it's been easy to track people if you really wanted for years.
Sorta yes, sorta no.
Yes GPS trackers have been around for decades, but the price of entry was - relatively - steep.
In the early days (90's to early 2000's) you basically had to buy them from 'spy' shops, and they weren't cheap, they'd cost at least as much as a low-end phone, $100-$200 or so.
Then you had to buy a SIM, and get an account (usually pre-paid) created, which costs more $ and requires much more effort.
Then they became cheaper and easier to get as places like AliExpress came along, and prices dropped to about $40, but then you still had to go through the hassle getting a pre-paid SIM for it, etc. But you generally still ahd to wait a week or 2 to actually receive the unit after buying it, enough time to cool off and think better of your revenge plan.
With the AirTag, you just walk into an Apple Store or even just the Apple section in an existing chain-store, pay you $40 or whatever it is, walk out with it 'register' it to your Apple account, no SIM for the device necessary since it doesn't connect to the cell-phone network as it piggybacks onto other already cell-enabled devices (iPhones).
It's the same as privacy problems around police surveillance. Sure, the cops could always see with their own eyes a person in public, or decide to follow someone in their car. But that takes manpower, time, effort, money to do. So it didn't happen often or on a long-term or large blanket-scale due to the cost of doing it. But as technology has evolved, it has become problematic due to the reduced barriers to entry. Want to follow someone? Attach a GPS tracker to their car, hell, buy 100 GPS trackers and tack them onto 100 random cars for the cost of a couple days work, and now you can follow 100 people for a month before the battery runs out. Or place a camera on a utility pole in front of someone's house for 6 months to monitor them, no teams of plainclothes cops sitting in cars or vans outfront, not even surveillance or wire-tap warrants needed. Easy. Don't get me started on ANPR and reverse cell-tower dump warrants and so on.
Apple has reduced the barrier to entry from a not trivial expense and effort, more than most people are willing to expend - certainly difficult enough to not be an impulse-buy opportunity, to a trivial amount of money and effort that a spur of the moment decision can implement in 20 minutes - "hey, I want to track this person, there's an Apple store right there, I can just go in, buy an airtag off the shelf, spend 2 minutes registering it to my Apple account, and dump it in their back seat all for $40 and 20 minutes effort most of which is waiting in line to pay for it".
Airtags have become a 'force multiplier' in the ability for the impulse-control-deficient to track and monitor their victims.