Front a-arm abnormality

[BOHICA-Chevy68]

so I had originally thought my frame was bent, or twisted somehow. largely based on a uneven stance and then I found shims mounting the upper A arm to the frame. they were to extend the A arm about 1/2 inch. however today I changed out the radiator support, inner fenders, and passenger fender. every part went on smooth and with even lines. I've never had one go together so easy before. I used the orig grill. in my experience if the frame is bent, this easy assembly would be very difficult. so my question is:
Why would someone shim the A arm?

I got the truck with its orig 140,000 miles. it's a inline 6 and had some damage to the front pass fender and bumper same side. all the damage is long on the fender. no damage above the bottom of the grill.

on a side note, I love finding the stupid half a$$ fixes my the inept prev owner. if you can fix cars or learn to do it right, don't do it.