> If I get pulled over in a Bentley with an expired sticker, I pay the same price as someone in a Kia.
The fine should scale with the size of the infraction. If you sticker expires on your car, the infraction is the same severity, no matter the car [0]. ~Hiding a few million vs. hiding a few billion in taxes is a whole different level.~ EDIT: They just hid it for information purposes. Not to avoid tax. Therefore, this does not apply in this case.
Also, the fine is intended to discourage the behavior. If the money obtained by breaking the law minus the fee is still positive, there's no incentive to stop breaking the law. $5MM on a fund worth a few billion is very likely to be well within the still profitable area.
[0] I'm not sure about the US, but at least in Germany, an expired sticker actually is a larger infraction for commercial vehicles, especially if you transport people. So even there it's correctly scaling with severity.