Nowadays it’s probably a performance / battery saving “feature” attempt.
When film is converted to 50 Hz TV, the film is sped up 24->25 fps and every frame shown twice. When converted to 60 Hz TV, there is "2:3 pulldown": every even frame is shown twice, every odd thrice. (Actually, both PAL and NTSC have interlaced video modes, with only every other line updated each frame, so as to conserve bandwidth.)
BTW, when 60 Hz computer monitors were introduced in Europe and used in office spaces with fluorescent lights with passive ballasts that flickered at 50 Hz, some sensitive users suffered headaches from using the computer screen for too long. These days, both fluorescent lights and LCD backlights tend to flicker at much higher frequencies that it isn't much of a problem.
[1] generally 24fps because that is culturally what film looks like and people get very weird whenever anyone tries to fuck with it
But actually interlaced content exists too. Each field is independent, there's no frames to speak of.
Early video game systems based on NTSC/PAL ran at 60 fps or 50 fps, but ran off-spec signals to always hit the same half of the display lines (odd or even). 4th gen systems (genesis/mega drive and snes/sfc) had a few games that used interlaced output; later systems had many, running PAL@60Hz became a common option too.