The main purpose of imprisoning white-collar crime is to act as a deterrent. If the upside for a financial crime is billions of dollars, and the potential risk is 25 years in prison, lots of people will be willing to take that risk, especially if 25 years actually means 17ish with good behavior.

If the punishment is life in prison with no chance of parole, it'll act as more of a deterrent.

Punishment lengths don't act as a deterrent to petty and violent crime, because the people commiting those crimes are not intelligent or are crimes of passion. Systematic fraud like this is slow, calculated and methodical.