There are a couple of possibilities.
One is that Seiko has returned to the capacitor technology and dumped the Lithium batteries.
Two would be that Seiko has built in to the watch a system that prevents the watch from discharging the battery low enough to cause it damage, which the 6 month batteries suffered a lot when people don't wear them enough to keep them charged.
A third one might be that it would take 6 months to hand wind the older batteries up to a full charge
One item not mentioned here is the PR indicator on the direct drive watches. It can be quite active at times and the power involved in running that part of the watch could be a factor in the reduced charge on these watches.