Does anyone have an idea why the plastic items in our cars don't hold up??

Which plastic pieces are you referring to? Engine compartment, body trim or interior trim?

Do you live in a state where there is a lot of sun?

I haven't had any problems with the plastic parts on my R55, but I live in the Pacific Northwest and I keep my MINI garaged.

Yes, I live in Central FL. But the car has a spot in the garage.

I've replaced all kinds of plastic and even vinyl pieces since I purchased the car new.
Engine plastic, rear brake light, interior plastic, vinyl stripes, windshield cowl etc.

Any big motors constantly running in your garage? Air compressor, fridge, freezer? Plastics don't like ozone.

The plastics can get brittle from the sun or the extreme cold, I just treat most with VRP from CG and it seems to help on the fading.

I have an air compressor but only run it once every 3 months or so. I do have a fridge in the garage as well but it's designed as an outdoor fridge so low run times and energy consumption. Gladiator full size fridge converted to a kegerator for homebrews!

Thanks for the product suggestion!
Any comments on the new F11?

Nice Grumman fighter jet from quite a while back.

303 Protectant is real good for protecting plastic from uv rays. I get it at West Marine.