Grocery store profits aren't larger than any other industry. Nor are they larger than in the past. Large grocery store chains do not have high profit margins. Sure, the total profit may be large if you run 1000 grocery stores.

What do you mean by they are the wealthiest in the nation? None of the richest people in the world built their fortunes on groceries?

Price fixing is a phenomenon. Anti trust is a policy agenda. What entity would carry out the proposed agenda, when the parties supposedly fixing are in different countries?

How long did the fixing agreement last successfuly? DRAM has famously gone through booms and busts where supply outstripped demand and led to very cheap prices and no profits.

OPEC worked about as well as any cartel. Could you give an example of a cartel maintaining their position without heavy government help? Even the drug cartels in mexico, with extreme willingness to coerce, cannot maintain a monopoly and have competed drug prices in the US down heavily! If you consider memory a cartel, then it has only remained so by... drastically improving the quality and reducing the cost of its product? Hardly a problem.