Well, firstly because you state "most" countries. but more importantly because the pricing should be clear and fair. Frankly even the biggest geek that spends time on FT doesn't fully understand the byzantine world of airline ticket-pricing so your average consumer has zero chance. There are plenty of examples around where airlines imply and in some cases erroneously state that fuel-surcharge is a cost outside their control (the implication being that someone else imposes it). It clearly isn't.

I'm not aware of any other product or service where the pricing is structured in this way. If I buy dinner at a restaurant I don't get a bill that breaks out a "grain surcharge" because the price of a specific commodity has risen that week (or to put it back into airline context, rose sometime in the last decade), I get a cost for the price of my meal. Fuel is a basic component that airlines require in order to get their aircraft and passengers from A to B, so should be part of the basic fare.

Let's face it, for the airlines to do this there must be some advantage to them doing so. If there is an advantage to the airline, then to my perspective there is likely to be disadvantage to the consumer.