CPI has been a big deal since last May.  That's when more than a year of higher, more stable Core CPI first began slipping under 2.0%.  Bond markets reacted with a noticeable rally in response.  When Core CPI fell further in June, the bond rally was even bigger and more noticeable.

From there, we see multiple examples of CPI setting the near term tone for bonds or at least causing one big day of gains or losses.  The chart below has 10yr candlesticks with most of the CPI release dates indicated as well as whether inflation came in stronger or weaker than expected.

Notice that November is in red.  This was one of the few examples of markets moving the opposite direction from the suggestion of the CPI result (i.e. stronger inflation, but bonds rallied).  Granted, traders could have been circling the wagons ahead of Thanksgiving, but either way, that was an informative rally, because bonds were willing to hold their ground in the face of data that suggested they shouldn't.  Sure enough, bonds showed an ongoing willingness to hold their ground for several weeks after that.  Of course CPI wasn't the only reason for that, but it certainly contributed.