I never would have understood this as a young, single person. Now that I have a family there are several times per year where we price out the cost of a solo ticket for one parent, the price of taking one or two kids, or the cost of all of us going for something. Having a quantity discount would absolutely tip the scales for us for certain trips. People will look at this as penalizing single travelers and want everyo…
A solo traveler can decide to take a trip because they saw a good fare very trivially: you're not going on a trip with 2 days notice just because a fare "tipped the scale" when you need 10x the planning and logistics, and the airlines know that.
They're not doing it to entice families to travel, they just know solo travel is associated with higher incomes and want to extract more money.