> Also airliners usually just become cargo planes for quite a long time before retirement.

Yes, but that's a function of how fuel economy and capital impact the overall economics.

Cargo = (usually) one flight per night.

Passenger = (usually) many flights per day.

It's important for cargo airlines to have low capital costs for an asset that spends a lot of time not making money, but it's important for a passenger airline to have low operating costs for an asset that's burning fuel all the time.

Passenger airplanes are repurposed for cargo when newer, more fuel efficient airplanes come on the market.