Could be because Autolite was part of Ford until 1973. Ford had been involved in anti-trust litigation over Autolite since the early 60s. The sale of Autolite to Bendix Corp (owner of Fram at the time) solved that. Since then the Autolite brand has followed Fram through a succession owners. Ford rolled out Motorcraft to handle aftermarket parts sales.
While Ford had Autolite/Motorcraft, GM had AC Delco, Mopar and AMC never had captive spark plug manufacturers. Never recall seeing a Mopar brand spark plug back in the day, all Mopars came with Champions. Back in the day when Mopar and Ford were slugging it out in NASCAR, both Autolite and Champion offered contingency awards as part of the total payout. Funny thing, IIRC, you didn't have to actually use the plug, you just had to have the decal on the car.