NFL oddsmakers may not be expecting Steelers QB Ben Roethlisberger to be playing against the Kansas City Chiefs. That's the only reason I can think of that the Chiefs would go from 2-point UNDERDOGS to 2.5-point FAVORITES against the Steelers on Sunday.
The idea of the Chiefs being a 2-point underdog to Steelers third string QB Landry Jones was a little surprising when the line first came out. The change in odds must have come some time in the past 24-48 hours because I checked earlier this week and the Chiefs were definitely 'dogs. Now they're listed as 2.5-point favorites according to most books.
Fans seem to be more down on the Chiefs than the oddsmakers. Ask any fan and they'll say the Chiefs are a bad team given their 1-5 record (and they're not wrong!). But each week the odds on Chiefs games are close. They were massive favorites over the Bears in Week 5, slight underdogs on the road against the Vikings in Week 6 and now favorites over the Steelers in Week 7. Andy Reid has said before that you're usually not as good as you think you are and not as bad as you think you are. That's probably the case here.
You can follow the Steelers-Chiefs line movement here.