I think Lincoln sales are getting hit by loss of foot traffic with the shutdown of Mercury.
However, a little perspective should be brought in to the Taurus/MKS sales. These vehicles are made in the Chicago Assembly plant, which, IIRC has a capacity of 200-250k vehicles per year. It used to team up with the Atlanta plant to produce Tauruses and Sables at a rate of ~500k per year at max rates. But those numbers are based on 3 shift production, and the Chicago plant is on a 1 shift schedule. That would put its production rate at 5,555 to 6,944 vehicles per month on a single shift.
In January 2010, Ford sold 3,768 Tauruses and 1,280 MKSs., for a total of 5,048 vehicles (about 1 shift)
However in December 2010, Ford added production of the Explorer on this line without adding another shift. In January, they sold 601 MKSs, 2,896 Tauruses, and 7,351 Explorers, for a total of 10,848 vehicles. Some of these were likely 2010 Explorer leftovers that were made in Louisville...
But you can see that they were likely constrained on capacity in the Chicago plant running a single shift, and may well have chosen to reduce supply of Tauruses/MKSs to support the Explorer launch, since the former have dealer stock available and the latter doesn't. (like all companies, Ford counts it as a sale when it leaves the plant, since it has been purchased by the dealer at that point). They're hiring and adding on a second shift, which should alleviate this constraint, and I would expect the sales numbers should recover once that happens.