For many years taxes meant just that, charges imposed by governments. It's easy to point fingers but I think the rot started when the US Government permitted the introduction of PFCs. These are fees charged by airports to fund the development of new facilities. They showed up in the tax box.
Then the EU decided to scrap duty free. The way I heard it, the airlines were worried that airport profitability would slip and that the airport charges would then rise. That, in turn, would force the airlines to increase their fares. Their argument was therefore to be open about who was charging what and split out anything that wasn't directly under the control of the airline and show it on the ticket separately.
At about the same time IATA, recognising the way things were going decided that the box in which these things were shown on the ticket could not longer be called just taxes and renamed it taxes/fees/charges. They also issued an edict that staff should refer to it in those terms but I'm not convinced that has been wholly successful.
All of the above refers to the traditional carriers. The low cost carriers seem to have 2 differentiators. Firstly they negotiate the lowest fees they can at airports and if the airport will offer a discount for not using the airbridge or some other facility they take it. But, more importantly, some of them don't seem to adopt the same attitude to splitting out all those taxes/fees/charges (although I have nothing to back that assertion up).
Things have now reached the point where (out of interest) I priced a midweek London/New York return and got a price of GBP126 plus GBP126.10 tax/fee/charge.
The low costs seems to have 2 differentiators. First they negotiate the cheapest airport fees they can, foregoing certain amenities that the traditional carriers take for granted, such as airbridges. Secondly, some of them have a different attitude to what they include in the fare and what they show as taxes. Mind you, that last paragraph is total speculation on my part.