The short answer is economics.
Also, whatever your complaint, we still have it way better than travelers before the airlines were deregulated in the late 1970s. Before competition drove prices way down, tickets were batshit expensive.
Also again, with the fees famously imposed by entities like Spirit Airlines, now we get to pick and choose the nickel and diming, rather than have it all thrust on us in one lump sum, un-itemized, like before.
Does all this make it any easier as you watch the total cost of the flight skyrocket between the search results and hitting ‘purchase’? Not really.