I think the Chiefs see it as an investment for Spags who in one year drastically improved the defense. They are keeping the core guys in Clark, Jones, and Mathieu together for minimum 2 more years (Mathieu's contract expires in 2021).
If Spags can churn out a top 10 defense every year with Mahomes at QB, they are easily Super Bowl favorites...and it's not even close. Chiefs might be going for first ever back to back to back SB Champion streak. Barring major injuries (especially to Mahomes), it is not an unrealistic possibility.