Why is my AirTag not updating its location?

Simple answer is that when your AirTag is outside the Bluetooth range (~30-40') of your iPhone, it relies on other iPhones that are participating in the Apple Find My network. If none are nearby, you will not see location updates.

Possibly because the battery is depleted? Apple only states that the tag's battery should last approx. a year with normal use. Placing it inside something will cause the Bluetooth beacon to "work harder," and the result could be more battery usage.

My AirTag is in my car-beneath the seat material. Not beneath the seat. It’s as close as it could possibly be to my phone-no obstructions-except the material on the seat. It isn’t below the seat, it isn’t behind the back seat, it’s in a spot no one would look for it, but if the car’s stolen, any dummy w a phone on them would ping it and it can be recovered quickly. It’s worked beautifully for about a year. As of the past few wks, it tells me when it’s home, how many hours ago it was last seen at home. Occasionally, it says my work location, but it should be able to be located 24/7. I’m not in a rural area. It’s less than 1.5 yrs old. Any idea why it’s not working???