I am pretty forgiving if someone snaps a pic and they didn't know flash is on, as long as once they see that they either turn it off or put the camera down.
There are so very few people who now have high-tech cameras (usually phones/tablets) thrust into their hands
that even have a rudimentary understanding of the gear's operation and menu-based controls.
Consider entire generations of people who simply NEVER figured out how to get their VCRs to stop flashing "12:00."
(Many even resorted to covering the clock face with tape.)
To many, the "little light" (AKA "flash") is just a part of the "way it works.",
"Oh, its always on. I take so many pictures and films (sic) that I don't even notice it."
They literally have no concept that it is controllable.
(Much less, that it is totally ineffectual at all but the closest-distance photos.)
To make an announcement that says to "turn off flash and/or video lights" just does not register with
uneducated or technophobe camera operators.
("If I 'change something,' it might not work anymore. I just leave everything alone.")
I can't tell you how many times I've talked with family members or friends who say,
"Oh, it's just always on." in regard to flashes and video assist lights.
"It came that way" is a standard line, too.
Many have absolutely no idea that the "no lights" announcement is meant for THEM.