Bank robbery typically involves violence or the threat of violence. I don’t think the two are really comparable.
To justify imprisonment (rather than purely monetary penalties or civil judgements) you really have to look at the relative scale of harm and the type of harm inflicted. Imprisonment doesn’t always make sense, there are many nonviolent crimes where a purely monetary penalty would be more appropriate. For one thing, imprisonment can prevent people from paying back the victim.
To justify imprisonment (rather than purely monetary penalties or civil judgements) you really have to look at the relative scale of harm and the type of harm inflicted. Imprisonment doesn’t always make sense, there are many nonviolent crimes where a purely monetary penalty would be more appropriate. For one thing, imprisonment can prevent people from paying back the victim.