Mostly for time synchronization. GPS/GNSS is cheap, widely available, and accurate down to nanoseconds, so it's displaced every other technology.

As an example, consider the blinking lights on top of wind turbines and other tall things. If you've got a lot of these in one area, the FAA recommends they blink in unison, to make them more visible and less distracting to pilots. Turns out the cheap and foolproof way to synchronize is to give each one a GPS receiver. This is fine until GPS goes down, and now something as innocuous as "blinking hazard light" is dependent on GPS.

This example fails safe if the lights fall out of sync ("oh no, anyway..."), but it's still emblematic of how widespread the problem can be.