Note that he hasn't actually been sentenced to 124 years. We're talking about multiple stacking charges here. You could get multiple charges of parking too far from the curb and it could add up to thousands of dollars, but that doesn't mean the parking fine is too much.
More than likely, it'll be reduced to a sane amount when the compile the charges. 5 years, maybe 10 (maybe more). The actual sentence (minimum sentences notwithstanding) is almost always up to the judge.
Yup, maximum sentences are actually generally there for the protection of the defendant; they put a ceiling on sentencing. Without them sentencing would be entirely up to a judge's discretion.
> Monsegur pled guilty to several charges of computer hacking conspiracy, for which he could receive a maximum of 124 years behind bars.
That's what a serial killer would get. US law is ridiculously tilt to corporations.