This is also the case in Italy as far as I know. I was a mailman for the Italian mail service for some months in the summer of 2019. We were encouraged to give priority to paid work (advertisement, other deliveries). Mail doesn’t make any money, it’s just a public service. Which is why the postal service also does banking and has its own mobile carrier. These things pay for the public mail service to work. Anyway this is the case in Italy so maybe it’s not relevant.