The crypto aspect stops apple form having data that is useful about you or your devices.
With respect to third parties tracking airTags the ID rotates so you cant have a continues track of a AirTag from other sources.
The ID rotation is governed by the private key of the tag, only the tag owner's iPhone has this so only that device can track a tag. Others can know a Tag was in the area but they cant track a tag over days between many locations.