Presumably inflation is not going to stay at 8% over the next 30 years.
In fact the current 30-year expected inflation is only at 2.2%: https://fred.stlouisfed.org/series/EXPINF30YR
In fact the current 30-year expected inflation is only at 2.2%: https://fred.stlouisfed.org/series/EXPINF30YR
Forgive me for my skepticism, but these guys are at best guessing. Most likely they are straight up lying.
So the data is partially based on market data (ie. implied inflation rate based on what the yield on TIPS is compared to treasuries). There's another data series for 10 year inflation that only uses market data and it tells a similar story: https://fred.stlouisfed.org/series/T10YIE. Since this is all market data, made by people who have skin in the game (ie. if they get it wrong they lose money), it should be less gamed the previous metric.