Working for one of the largest employers is not the same thing as working for a company that has the largest number of employees who travel. Sites online say that Walmart is the largest employer in the US with roughly 2.2 million employees. It's just a guess, but I imagine that very few of those folks travel as part of their job.

From my experience working in hotels, I know that chain-wide corporate rates are basically a numbers game. Once a company hits a certain number of room nights (measured in thousands or tens-of-thousands), they start getting discounts. Those discounts are usually percentages off of the rack or standard corporate rate. Where I was, the maximum discount was 20%.

Individual hotels were encouraged to offer larger discounts (or set nightly rates) for companies that provide significant business at the hotel. Those rates are tied to the "code" that is used at the chain-wide level. A single code makes life easier for the guest and also allows the chain to easily track the amount of business provided by the company.

Certainly, there may be some of the unusual conditions that RogerD408 and CJKatl mention at play. But, the simplest explanation could be that your company doesn't provide enough business to Marriott hotels to warrant any discounts. If another chain provides higher discounts and you booking engine steers you to those hotels, I wouldn't expect anything to change.

Although I concur with the opinion that you shouldn't take it upon yourself to contact Marriott, I will say that the people in charge of this area would be at the National or Global Sales Office.