It's a calendar spread. Last year, you were buying 2021 dollars for a fixed rate (2.675% APR in my case), but you different vintage dollars over time. You owe 2022 dollars in 2022, and 2031 dollars in 2031. A 2051 dollar is almost certainly going to be worth significantly less than a 2021 dollar.

So you're buying 1 2021 vintage USD, but at the extreme, you're paying it back with 2.2 2050 dollars. If we expect inflation to be an average of say, 3% over that period, each 2021 vintage USD should be worth at least 2.42 2021 vintage dollars. So in this example, you're earning real dollars over this period.