Most TVs and monitors have a fixed refresh rate, often 60 Hz these days.
If a game runs at, say, 48 FPS, some frames would be doubled every second, and some won't. The resulting video would seem more jittery compared to 15, 30 and 60 FPS, where frames can be doubled or quadrupled evenly.
That's why FreeSync and G-Sync monitors are a big deal to enthusiasts, they avoid this issue for their refresh rates are exactly what's being rendered.
But every modern TV today are not at 100 or above ?
Some monitors are 144 Hz. Plasma TVs were claimed to be 600 Hz but that's not your everyday performance.
But most are locked to the conventional 24, 30 and 60 Hz. Sometimes you have 50 Hz. It depends on the resolution and the model.