Freighters

The “Finnair”s MD11’s” thread made me wonder.

Most of the airlines arenow phasing out their MD11 , DC10 , A310 ,B742 or B743 even B767.

However the cargo airlines such as FedEx are catching any MD11 available on the market.

It seems to me that the cargo business is much more profitable than the pax market.

Is it the only reason?
Did I miss something?