You're taking a leap of faith that the defense is going to perform and/or not combust when the offense sucks and the HC gets fired 5 games into the season.
I'm not saying coordinators don't make a living off of taking 1 year gigs. But if you're looking for stability and no risk, then there are better positions out there. There are 6 or 7 new HCs out there this year looking for a coordinator and they'll give them a multi-year contract more likely. It might just be me, but I'd prefer to look there.