I'm guessing since they are grass fed, there is not much fat or flavor. They tried leaning it out more, but it was just dry and tasteless. This is I believe why it is 85/15 mix.
On another subject, I have been craving a good drive thru burger for months. Last Monday, I drove to a local great place, where I ordered a 1/3 pound burger, small fries and a small drink. Cost me $10.20. That's not the issue. This 1/3 pound patty was 4" in diameter, and about 1/4" thick. It looked and tasted like shoe leather. They placed this patty into a 6" diameter bun, loaded it with 1" of shredded lettuce, added a thin slice of tomato, so when I opened it, it was huge. I took 3 bites until I actually tasted beef, or whatever that shoe leather was. I feel this was more of a lettuce burger, with a small salami sized meat patty within it. I know everyone is cutting back to save pennies, but F that, never again will I go to Jim's Burgers.