All the traffic lights here in Australia are honking great big metal poles that you'd need some serious equipment to reposition. Swapping bulbs would be a big operation too.
What country are you in that has rotatable traffic lights?
I'm in the USA. This particular incident happened in Washington, DC. I also saw a driver do this once in Palo Alto in Silicon Valley.
Anyways, even if lights are too big to climb up you can put on a yellow vest and get a flashing light on your van and people wouldn't really think twice.
I hopped on Google Street view near the central core of Sydney, and it looks like at least in certain areas you all also have lights like that are close to the ground and easily accessible. I'm guessing in more suburban or rural areas the signals are higher up (which makes them easier to see from a distance while driving faster).
Even if the traffic lights can't be rotsteted it's relatively trivial for an bad actor to break it in some way and hanging up your permanent green light at night and then watch the chaos.
As gp said: The amount of such bad actors is low. And gains from an individual hack are low and there's a chance of getting caught.
"Relatively trivial" must be relative. Traffic lights where I am require a cherry picker in the intersection to get at.
This is like hacking servers. If you can get all the way to physical access with the device, of course it's exploitable. But that doesn't actually say a lot about how secure something is.
I imagine the quality of the lights around the world differ. If you can climb up and adjust it, these aren't the kinds of lights I'm thinking of.
So you'd need some equipment to do anything to them. And that equipment would have to basically shut down the intersection. So do it at 4am and hope that nobody drives by for the half hour you're there.
What country are you in that has rotatable traffic lights?