Little cropdusters and sport aircraft are who the anticollision lights are designed intended to protect, and many of them are not ADS-B equipped.

In the US, ADS-B is not required below 10,000 feet and when more than 30 miles away from the 30 largest commercial airports.

This is a safety measure. You can't rely on ALL aircraft having functional (or installed) transponders. You must actively sense incoming craft because they don't always politely announce themselves.

At small unattended airfields, you can sometimes turn on the field lights by transmitting on a particular frequency (as if you were calling the non-existent tower in quick succession).

https://www.aopa.org/news-and-media/all-news/2017/march/flig...

(Of course, in this case it works because the pilot already knows the airfield is there.)

The FAA document says "sensor-based" but every installation I have seen in the US uses radar.