Because it costs extra money to do that test when you send it to the state lab, so most likely to keep costs down. I would imagine that to most Elmer Fudd's, they just want to know how much lime and 10-10-10 to add to their plots and wouldn't be willing to spend the extra to know the OM.
I used A & L Great Lakes Labs on a suggestion from Doug Galloway, very good information. More expensive than Biolgic or Whitetail Institute, contacting them before sending in samples, find out cost and info on samples.
I bet it's the cost. To measure OM, they have to put a sample of dirt into an extremely high temp oven and burn off the OM, and then reweigh it. I sent mine to AgLab Express in Sioux Falls. I got my N/P/K, soil Ph, buffer Ph, and OM for $20 along with recommendations for the crop and method I was using.
Yup, just multiple your actual plot size by 10 to keep the math simple and make you look more important. If they give you slack about it being a food plot tell them your an organic farmer. The Uwextension raised there prices too, and I pay enough in taxes, so a little white lie doesn't hurt anyone besides Scott walkers reelection campaign.
The guy i dealt with at Aglab Express in Sioux Falls was great. He gave me a tour of his lab and showed me how a soil test was conducted from start to finish. I told him I was no-tilling a food plot and he still treated me like the governor. I couldn't get him to quit talking. He even offered to help me get in touch with a cover crop specialist at SDSU for the additional questions I had.