That's the problem - aside from only being sampled every 6 months, shelter reflects what people are actually paying, which includes a large number of people who

That's the problem - aside from only being sampled every 6 months, shelter reflects what people are actually paying, which includes a large number of people who haven't renewed their rents or who paid a lot less for their home and have no idea what it'd rent for now. As these people renew their leases or seek new housing, they're going to have to pay market rents, which in many cases have gone up a lot more than the measured CPI component. That bakes in a large future increase in the CPI, simply from price increases that have already happened.