What might have happened to degrade postal service between Paris/Savoy and Venice between 1500 and 1765, from 2 weeks to about 3.5? Could it have been possibly

What might have happened to degrade postal service between Paris/Savoy and Venice between 1500 and 1765, from 2 weeks to about 3.5? Could it have been possibly been Switzerland leaving the HRE (and maybe imposing border duties) in 1648?