I think the main reason the US throws people in prison for extended periods for petty crimes is if those crimes were repeat offences - so you have ridiculous situations where people serve years behind bars for stealing toothpaste.

This case is kind of odd though, as the perpetrator committed the same crime many times over a quarter of a century. The items stolen were also of great cultural value. So here we have a person who has repeatedly stolen cultural items, yet they get a very lenient sentence - I very much doubt the sentence would have been the same had he been a black man from a working class family.

This case really highlights the two-tier legal system that exists in the US.