They even might? It's not unheard of for Apple to release software on other platforms, however uncommon it might be. It's certainly not the kind of thing they do right at the time of release.
I don't imagine you'd get much penetration relative to running it on every device at the OS level, though. Probably rough on the battery running in userspace?
It doesn't seem like it solves a problem most people are likely to have.
People are not going to use AirTags to more effectively stalk people than the existing GPS trackers on the market. GPS tracker would be much better in fact.
AirTag: Very economical (no monthly fee), 1 year battery life, no line-of-sight required, easily purchased without attracting attention or providing an address, unguaranteed data freshness, size of a coin.
GPS tracker: Monthly fees, 1 month battery life, line-of-sight required, slightly unusual thing to purchase & may be difficult to obtain without supplying an address, usually better data freshness, at least as big as a box of tic tacs.
It's not that AirTags would always be ideal for stalking, but considering the ease of availability & use, it's definitely going to happen. The most interesting part is that Apple decided to release this product. It's only a matter of time until AirTags are linked to a case of stalking (whether the best device for it or not) and when that article gets written, it's simply not going to be aligned with the brand image they typically aim for.
The latter isn't something under the stalker's control, it's just a really poor tool for that particular type of antisocial behavior.
Plus it's tied to your Apple account, so we're talking about getting a fresh iPhone and ginning up an account, or leaking exactly who is doing the stalking.
The number of people who will try it isn't zero, we don't live in that kind of world. I don't picture it going very well for them.
iPhones can be grabbed used for fairly low prices, same for Apple accounts.