They have HUGE pixels so they can crank the brightness while still being able to cool them. The ”just“ use LED matrices. It‘s almost completely different from how normal displays work.

Isn’t that basically exactly how an OLED screen works? What’s different, except that it’s made from discrete components and not integrated?

That's a pretty big difference, isn't it?

Separating the power-bits* from the light-emitting bits (even just to have them on opposite sides of a PCB) lets each of these bits dissipate more heat.

The nature of their use (where we only generally pay close attention to huge outdoor screens occasionally) also has lets the big, bright outdoor displays get away with artifacts (like sometimes-noticeable scanlines, or terrible color gamut) that just won't fly on a TV that is meant to be watched day after day -- by the same small group of people -- for years.

(*No, OLEDs don't switch themselves on and off; they're still just diodes like other LEDs are. There's transistors integrated into the panel to do that part.)

It’s different, but I wouldn’t say “It‘s almost completely different”. It’s like comparing a marine diesel to a diesel car engine. It’s different but it’s still the same principle.

Perhaps so. In terms of engines, the relative scale certainly emphasizes the point (we all know about how big car engines and OLED screens are, but it's hard to comprehend the vastness of a big marine diesel engine even while standing inside of one on a ladder).

One has transistors that can't really be seen with the human eye (TFTs), and the other has transistors in SMD packages that can not only be seen, but also kicked and replaced when needed.

And one has tiny [O]LEDs that are integrated tightly together into one unit (which must be replaced at one time in the event of a pixel failure). The other has relatively enormous PCB-mount LEDs (which can be serviced individually on a bench by a tech of sufficient skill), which in turn are mounted on modules that can be swapped by a field tech fairly rapidly.

They're very different in construction methods, just as car engines are different compared to big marine engines. They'd also appear rather similar in function if one were to draw a block diagram of each.

Also the modularity/repairability aspect.

For a junior display, you can have some guys with hand tools swap out broken modules in a giant outdoor display, but doing the same kind of repair stuck pixels in a few thousand living-room screens is a no-go.

That changes the trade-offs in terms of performance versus expected lifetime.

That is the main difference, but it is a huge one. The manufacturing process is utterly different, and the components are MUCH bigger.