Although they are conceptually similar to a Tile, AirTags have far more stalking potential. A Tile that isn’t near you can only be tracked if it comes into proximity of someone with the Tile app open and active on their phone.
However, an AirTag’s location can be tracked any time it comes into proximity of any iPhone. The number of iPhones out there moving around in the world is substantially higher than the number of phones with a Tile app open and active. iPhones form a massive tracking network for AirTags that can be quite difficult to get away from.