Severe inner tire wear cause

My '04 Expedition 4wd is exhibiting inner wear on rear tires. An alignment was performed but was fine. I'm wondering if the coil springs are the most likely culprit. Would marginal/faulty shocks also contribute to this problem?

Poor shocks tend to produce a 'cupping' wear pattern. It makes the tread of the tire look bumpy or wavy.

Even wear on the inside is always alignment oriented; specifically the camber is incorrect. If the camber is way off there is usually a specific cause that needs to be corrected, like worn suspension bushings or ball joints or a bent component (accident damage, severe off -roading etc. )

You had a shop check the alignment, right?
Did they actually DO an alignment, or did they say NO alignment changes were necessary? Did they actually place it on their alignment machine or did they just do a visual inspection?

IMHO anything that causes such severe tire wear will be noticed by a shop IF they actually place it on a machine. However, to do such this check they will have to charge you the money for an alignment.

I took the Expedition into a shop for a look. The alignment was off and the springs were two inches off. The shocks were replaced also.