I don't know what the back-story is.  All I know is the highways in So Cal really are the worst in the country.

 I used to think that the roads up north, what with frost heaves and potholes were bad... and they were, don't get me wrong.

But the Cal Trans crews that pave the roads in So Cal must try to make them as non-smooth as possible.  If you get a patch that has less than an inch of variance with the road next to it, count yourself lucky.  And, if you somehow find an overpass that doesn't unload your suspension, and sometimes even leave you airborne, again... count yourself lucky.

It isn't until you get 100 or so miles north of the 210 freeway that things even get a little better.  Heck, even the smooth roads feature this little undulation that has tire carriers smacking against tailgates for hundreds of miles.

Check out the picture... I was on the 5, with an empty trailer...every time I transitioned from a light patch to a dark patch the trailer wagged the Grand and it was so loud I couldn't even hear myself think.  This is normal for here.  This is our tax dollars at work.