As an outsider that knows very little about this company, yet I did attend the annual meeting one time in the past few years, my thoughts at the time were that much of the GRIF earnings power were spent on corporate expenses (executive pay, etc) and therefore the underlying asset values were not of much use when the earnings are handed to others instead of common shareholders.
A cursory look at the trailing FCF and market cap show me a yield to equity of around 5%. $10 million in FCF to equity and $200 million market cap. Clearly this cursory look is not in-depth and my assumptions may be far off, but that's how I view the company and therefore are not surprised it trades where it does. I'm sure this board has discussed many things that would make my analysis wrong, but that's my donation to the GRIF discussion if you'd like them.