I don't understand why "on-ramp" metered lights aren't used in many more places. Like enforcing easy zipper merging. Put lights on both lanes that need to merg

I don't understand why "on-ramp" metered lights aren't used in many more places. Like enforcing easy zipper merging. Put lights on both lanes that need to merge together, out there in the middle of the freeway. Turn them off when there's no traffic.