I have worked on government payroll systems, simplifying those rules is almost impossible from political PoV. They are generally a combo of weird laws, court cases, union contracts and more.

Any time you think about touching them, the people who get those salaries come out in droves and no one else cares so government has every incentive to leave them alone.

You could simplify them if you made sure the people getting them got overall more money ;) The government doesn't want to do that though.