Why is AirTag location no longer updating?

My AirTag fell off my key chain without me noticing. I did not notice until I had already driven away.

It must have fallen off near a beach area.

I put it in lost mode as soon as I realized. It would update and showed it was in the same location for over 24 hours.

Then I checked that afternoon and it’s in another town 30 miles away from the original location. It updated twice at that location and now it shows the last tracking was 5 days ago. Location never updated again.

Why is this? Should I keep in lost mood or just remove it? What is causing this? What should I do? I know I am not getting it back