The colorblind cannot see red and green lights, so light color cannot alternate. Flashing also triggers epilepsy, so we probably should not be adding more of it to roadways. Bright lights are also hard to see in sunlight.

Flashing lights draw your attention, and you would not want to draw attention toward wrong-way signs unless the driver is actually looking to go the wrong way. Stop and construction signs make sense because 100% of passing drivers in either direction need to notice them.

These devices use power and electronics, which cost much more to build and maintain.

The message is confusing. You cannot tell what hazard is actually moving downward, so lights=car flow would need explained textually. The lights are falling downward but the hazard is coming at you, which is a message that is easy to misinterpret.