50Hz is what European power runs at, as opposed to North American 60Hz. This had some correlation to the analog film frame rates being 25 fps in Europe and nearly 30 fps in America, though I’m not entirely sure what the cause was.

Nowadays it’s probably a performance / battery saving “feature” attempt.

Standard CRT TV refresh rate in the UK. Pretty much all home computers here produced 50 Hz output, the goal being that they could be connected to a TV, until the PC started to eat that sector in the early 1990s. Games consoles supported 50 Hz (same rationale) until at least PS2/Xbox.