and it's against the law.

Likewise, a seller can't charge whatever he wants even if he has a monopoly. Sellers want to maximize their profits, not necessarily to charge whatever the market will bear. Most products have elastic demand. If the sellers try to charge too much for a product with elastic demand, then sales of that product will decrease. For example, a store might try to charge $20 for an ice cream cone. Suppost that cone cost them $1 to produce. In this example, the seller could make a hell of a profit on each one sold but he won't sell very many of them. On the other hand, charging a more reasonable price like $2 or $3 for the cone would lead to much higher sales and higher profits.

Some things like gasoline have relatively inelastic demand. For the most part, consumption doesn't drop very much as the price increases. Back in the 1970s when the price of gas doubled in 1973 and again in 1978, many people bought vehicles that got better gas mileage. However, as the price of gas stabilized and even dropped in real terms, gas mileage became less of a concern when buying vehicles.