That's because they started facing good teams in the 2nd half. Tua had some of the most time he's had all season in KC playoff game (2.32 seasonal average vs 2.52 in playoff game) and was pressured at a rate (14%) less than his seasonal average (15.7% PFR). It's not about time. The pass blocking isn't really important to this offense. If they thought it was, they would have gotten a different center.
Folks want to blame the line, but it's really much more complicated than that, and I got news for you people. The pass blocking isn't getting any better next season.