So over time the material starts absorbing dirt particles. Just from dust and what not in the air it’s impossible to stop dirt from eventually penetrating. Even if you’re washing the car every single time you’re eventually going to get some dirt in there.

The dirt in combination with the friction from the cover itself will slowly wear the clear coat away.

This is why it’s ok to use a cover for long term storage because you’re seldomly removing it. Where as taking the cover on and off all the time will do more damage than good.

Keep your car waxed. That’s all you need.