There are a few reasons why lowriders are illegal in California. The first reason is that lowriders often have hydraulic or pneumatic systems installed which allow the driver to control the ride height of the vehicle. These systems are not allowed under California law because they can be used to make the car bounce dangerously while driving.
Another reason why lowriders are illegal in California is that they often have extremely loud stereo systems installed. This can be a distraction to other drivers and can also lead to noise pollution. Lowriders also tend to have very bright, flashy paint jobs which can blind oncoming traffic at night.
Lastly, many lowriders have large spoilers or other aerodynamic modifications which can make them unstable at high speeds. This makes them more likely to get into accidents, and thus they are not allowed on public roads in California.