I am a natural skeptic, but in this case I think it is just an accident of history how different systems developed.

FWIW, although this is not well known, many medical schools offer combined BA/MD degrees, ranging from 4-8 years:

https://students-residents.aamc.org/medical-school-admission...

When I went 20 years ago, my school did not require a bachelor's degree and would admit exceptional students after 2 years of undergraduate coursework. However I think this has now gone away everywhere due to AAMC criteria