Considering he's not a physical threat to society, only an intellectual one, I'd much rather he be slapped with a financial punishment large enough to be meaningful.
In which case we've just set up a punishment system where poor people go to jail and rich people don't.
OK, so require community service. That doesn't cost me as a taxpayer, and even benefits me indirectly. Community service is also a far better rehabilitation strategy than locking people up when they aren't a physical threat.
Or delayed financial punishments that are proportional to your earnings in the future.
One could make a good case that this is already the state of the justice system in the United States. The simple act of being able to afford a better attorney alters the outcome of a trial.
If a criminal is violent and needs to isolated from society or needs rehabilitation programs skills training etc to live a moral /legal life then perhaps prison can offer those .
Even with traditional non white collar crimes , like say prostitution or small drug dealers offender are often victims as well , putting them in prison is counter productive.
The punishment philosophy is based on the premise that punishment is an deterrent and severe punishment will make people not break the law. This is outdated view.
Decision making when committing a crime is not driven by fear of imprisonment. People do not always make rational decisions , especially under the influence of a substance . our risk perception and tolerance is not statistically optimal plenty of games and tv shows revolve around this .
Logical reasoning arguments aside , on pure numbers rate of incarceration and convictions, recidivism per capita in the U.S. is by far the highest in developed economies and the difference is very stark compared to say Norway where rehabilitation is the focus, famously prisons are so empty they rent it out to other countries, a mass shooter complains about not having access to latest play station.
I am not even touching on the problems with the slavery , for profit incentives , the dis proportionate racial representation , racial /economic sentencing biases for similar crimes in the U.S.
That's a great point, he should be sent to work in the uranium mines of Kamchatka to earn his keep for those 27 months.
The non-snarky answer is 'because sentencing in this country is a mixture of rehabilitation, punishment, and public safety', with a very heavy emphasis on punishment. (And quite frankly, I could think of more sympathetic persons and sentences to raise your question in defense of.)
Q: Why do we (or should be) putting rapists, thieves, murderers behind bars?
A: Because I'm happy to chip in and pay for their locked-up housing and food to make sure that they're not on the streets hurting people.
But this guy? I don't give a damn about him. He's not a threat to me, my company, or anything I'm involved with, and I shouldn't be paying for his punishment or rehabilitation costs.
If this guy walked past my home at night I wouldn't give a damn. If Brock Turner came anywhere near my home or friends' homes I'd be scared. Which of the two really should be behind bars? Why is this harmless-to-me guy being locked for 27 months at MY expense but Brock Turner getting 6 months?