Here is a toy example showing how this works out explicitly
Suppose we have a flight that goes from New York to Maco Georgia via Washington DC.
Suppose further it costs $16,000 to run a 100 passenger plane from New York to DC and another $12k to run the same plane to Maco GA, for a total of $28k
There are 50 executive businessmen who need to be in DC on a schedule and are willing to pay $300 to get there, there are also 50 people who want to visit there parents in Maco but only if they can get there for $250. Additionally there are 25 people who want to go from DC to Maco for $100.
So selling all of the tickets, the get 50x$300 + 50x$250 +25x$100 = $30,000 so everyone gets a price they can afford and the airline they makes a profit of $2000. Everybody’s happy.
But those executives decide to skiplag, then the airlines earns 50x$250 + 50x$250 +25x$100 = $27,500 and ends up with a $500 loss, not good.
Suppose instead they decide to change the pricing structure so that New York to DC and New York to Maco both cost $275. But then half of the passengers visiting their parents decide its not worth the money. So they end up with 50x$275 + 25x$275 +25x$100 = $23,125 for an even worse loss of $4,875
So finally they decide maybe to keep the $300 fairs and drop the Maco run as unprofitable. Well then the New York to DC flight is only half full and so they only bring in $300x50=$15,000 for a flight costing $16,000 so a $1000 loss.
So the solution for the airline is to drop the flight entirely and everybody loses.