I have zero background in chemistry, so this may be a dumb question: but if the issue is it not lasting 12 hours, why can't doctors halve the dose and prescribe it twice as often per day?
Because the 12 hr formula was part of a huge marketing push to reduce doctors' "opiphobia" and get them to prescribe more. Doctors were likely unaware of the roller coaster ride of withdrawal they were sending patients on.
I believe the patent extension to keep it from going generic was predicated on the 12 hour, slow release, dosage.