Even flicker that isn't perceptible to humans is still associated with increases in all sorts of things including eyestrain, headaches, anxiety, migraines, and seizures.

150Hz is well below the human perceptual threshold but still within the range that can cause problems.

Because people can see the flicker. It becomes apparent with object moving quickly across your visual field (including waving your hand left-right). It creates big issues with photography and video recording.

Flicker at certain frequencies isn't noticeable to humans in isolation. Add in other types of flicker (lights at other refresh rates, monitors, TV's, etc) and you can see the interference between them.

Because of the rather well documented effects on health and visual performance.

When a bright light is extra annoying to light sensitive eyes it's because the lamp is actually blinking at a high frequency.

Because cities are made for people to live in.