There have literally been cases where a passenger has seen an engine catch fire and notified cabin staff, and the pilots did not yet know it was on fire. Or when a passenger's testimony has helped when the instrumentation was telling them the WRONG engine was on fire.

The concern during takeoff and landing, however, is this:

You need to evacuate the plane. The left side engine is on fire. You don't want to evacuate onto the left wing. Having all the shades open greatly increases the chance of somebody (passenger or cabin crew) seeing the fire, quickly, and ensuring a speedy evacuation through safe exits.

Which, no, it doesn't happen often. Flying, these days, is very safe. But when it does, it's a small thing that costs nothing that can help.

(Also, articles don't have to benefit people to be interesting. Feel free to apply that standard to your own work, but not to other people's).