I find it humorous that the FAA mandates retiring from a 121 cockpit while the cockpit of a 135 ops can fly FOREVER. Heck, some 135 ops use the same aircraft.
Why? Money and public perceptions. Cause it's big news when an airliner crashes and kills hundreds while a biz jet kills tens.
117 rest rules apply only to 121 pax ops and not cargo. Why? Money and public preception.

It is about money! Then public perception.

If the feds truly wanted safe air travel then 121 and 135 ops would be one reg, one retirement age and one rest rules. ATP and COMM ratings are same for 135 and 121 ops. If different worlds in 121 vs 135 then why not different certificates and/or certifications of pilots?