Fines are a slap on the wrist. But take away freedom from the guilty and things will change. Quickly.
Robbery is a violent crime (robbery, by definition, consists of using force or threat of force/intimidation) that places members of the public in danger. For example, last month there was a Nigerian bank robbery last month where bank robbers armed with assault rifles and got into a gun battle with police officers that left 16 people dead. [1]
Now, you could make the argument that running around with an assault rifle and firing at people is its own crime, but when you walk into a bank and hand the teller a note that says "Give me all the money in the vault," you are stating by implication that you intend to do [very very bad thing] to them if they don't -- you are using the implied threat of violence. (By the same token, if you confront people in an alleyway and say "Hey buddy, give me your wallet," you can't defend yourself in court saying, "But I never threatened people with violence!" The threat of violence is implied by your demand.)
So, in your question, you ask why bank robbery (a violent crime) is a jailable offense, while wage theft (a white collar crime) isn't. I think there's a lot of support for the idea that "non-violent offenders don't belong in prison (but violent offenders do)."
It's the same reason that burglarizing your neighbor's house while they're on vacation is considered by most jurisdictions to be a less serious crime than mugging someone: robbers don't just victimize people by taking their money; they also threaten the victim's physical safety. I personally would feel much more rattled if I had $200 in cash taken from me at gunpoint than if I had a client stiff me for $500.
[1] https://www.cnn.com/2018/04/06/africa/nigeria-bank-robbery/i...
And yet you'd still go to jail for doing that. Potentially for several years depending on the value of what you stole.
Wage theft orders of magnitude larger than that burglary would still typically only get a slap-on-the-wrist (relative to the ill-gotten gains) fine.
To turn your attempt on its head: why is robbing one person an offense that gets incarceration, but robbing a hundred people may not even get you prosecuted?
In the latter case (where you describe "robbing a hundred people"), are you referring to wage theft? Because if the employer is not using violence or threat of violence, then by definition they are not "robbing" people.
That was the entire point of my post: theft and robbery are not the same; robbery is theft + use/threat of violence.
And then you used the analogy of breaking into a house when nobody's home. And I pointed out that carries stiffer penalties than wage theft, despite not involving the use or threat of violence against a person.
Your attempt to split hairs to justify the near complete lack of punishment for wage theft is not succeeding.
As I said earlier, put people in jail for theft and fraud and you'll see those things decrease. As it is now, too often (white collar) crime __does__ pay.
If you purposely under pay someone, you are:
1) devaluing them as a human being and a citizen
2) you likely could be putting them under excessive stress due to lack of income.
3) if they are (mostly) minorites it could be argued that your decision is racism.
Etc.
Given what we know about the mind and the body, the gap between physical violence and emotional violence is becoming less and less disticnt. (Note: Studies have found the memory and effect of emotional abuse last longer).
It is at this illogocial to priortize one over the other. Theft is theft. In both case there are "side effects." In fact, I'd argue your better off witnessing a bank robbery then being subjected to wage theft.
None the less, fines are a slap on the wrist. Look at Wells Fargo. Disgusting. They say crime doesn't pay; unless of course your collar is white.