While the AirTag isn't a ideal theft prevention method, it's an easy and cheap solution imo (especially in combination with S-PIN). I'll make mine soundproof, so it's not too obvious where it's hidden.
If the car gets stolen I - hopefully - have two ways to track it.
Also, if it's that easy to check if a car has an AirTag, perhaps they'll skip those instead. Maybe it's naive to think but dismantling the car & alarm
and check for an AirTag does seem riskier imo

My car is parked in a parking lot, so keyless entry probably won't be an issue (except when parking somewhere else obviously).