Why would they trust "a random blinking green light", but not a written and stamped order? Yes, they could do that (and sometimes it will actually prevent an accident), but it will be more being a snowflake, then being a decision for safety. A conductor is simply not responsible for whether it's safe to drive on a given track. Their equivalent is not a car driver.

The "random blinking green light" is generally more reliable

Being a snowflake here has 2 benefits:

1. Getting company managing tracks to fix the lights (they need to deal with angry customers and pay off damages for delays and more), so there's a direct path from unreliable lights to economic damage.

2. Avoid crashing and killing yourself and passengers on the offchance the person on the radio is a moron