The conclusion is about cost, so the quality of service is irrelevant.

This year, (fractionally) some of the customers who previously paid full-fare have switched to receiving a discount. If both prices are constant, people now generally spend less on tickets. We already knew full-fare was constant; (B) adds the missing piece, discount constancy.

We already knew that Toronto-to-Dallas full-fare prices were constant, and that route is the subject of our conclusion. Whether prices for other routes have changed is irrelevant, and doesn’t resolve the gap (potential discount price changes) we identified.

The conclusion is about the average price people pay for tickets; the total number of people paying for them doesn’t affect the average. (If a cup of coffee always costs $3, the average spent per cup is $3 whether 10 or 10,000 people buy coffee.)

The conclusion is about spending, and we already know the proportion of passengers with discounted tickets. So how the discounts are offered is irrelevant.