The other consideration in the long term is the demographic spread of the pilot workforce where ideally the bulges (retirement year/s) do not exist.
The last weight restriction to be removed was for the SENIOR COMMERICAL PILOTS LICENCE which required 900 hours experience with the ATPL exams passed for issue. That allowed pilots to be in command of ac up to 20,000kg.
Last issued in 1989, with a transition period of 5 years for holders to upgrade to the ATPL or revert to CPL.