They have only so many tickets, they need a way to determine who get them, so they use price to solve the scarcity problem. They could use other ways, but that would mean less profits and maybe unfairness somewhere else. It is not fair for everyone but it ranks on the low end of injustices.

But I think I see your larger point. Imagine if this was not concert tickets, but a sudden food shortage. We already see it with housing and medical care. Solving the scarcity problem by price alone can get really unfair and dehumanizing in a hurry.