Murder might be for 0 money, but the sentences for that are even higher.

The harm of robbery greatly exceeds the monetary cost. It's right and proper that violent crime should carry much higher sentences than nonviolent crime (and that's before we get into how much less clear-cut these white-collar cases usually are).

Robbery is a violent crime. It's distinguished from pure theft by the use of force (or the threat thereof), which is why it is punished more harshly.