The number of HDDs sold has been in decline for over a decade. I doubt there is massive appetite for expanding production capacity

On the other hand the total storage capacity shipped each year has risen, as a combination of HDDs getting larger and larger, and demand shifting from smaller consumer HDDs to larger data center, enterprise and NAS HDDs. I'm not sure how flexible those production lines are, but maybe the reaction will be shifting even more capacity to higher-capacity drives with cutting-edge technology