Jaime Hernandez: In 2005 the U.S. Mint introduced Special Mint Sets which contained an example of every circulating coin in a special Satin Finish. It appears that the U.S. Mint was more focused on producing high quality Satin Finish coins than for circulating coins. As a result, 2005P and D circulation strike Lincoln Cents were made of poor quality that even examples in MS65 or MS66 quality were difficult to come by in circulation.
Examples in MS67 were very scarce with a few hundred examples turning up despite lots of searching. In MS68 they are very scarce with less than a handful of examples known and none being finer.