4. Lincolns cost more
5. Lincoln was merely easier to "sell" to the other Powers That Be ....... especially since few-if-any people in FoMoCo understood EITHER of them, #4 was something they could 'hang their hat' on
and which was easier to 'show' as not fighting with the OneFord theory for the Ford Brand &
6. Lincoln actually has fewer & more simplistic ICONS in their lineup history - so fewer "toes" to get stepped on (TownCar, Mark, & Conti are way more "Dummies Guide to Luxury" than the Cougar(s)
let alone LeadSleds, Montego, Sable, Capri, Marauder, Mariner, Mountaineer, GRAND MARQUIS, 'Broughams', Park Lanes, Sun Valley, Turnpike Cruiser, Monterey, Meteors, MESSENGER, Lynx, Bobcat, Comet, Topaz, even Monarch & Tracer...
...intentionally omitting a few)
ps here's the link: Mission:MERCURY!