Because when you consider the long history there and the current lineup of Chevrolet teams, I doubt that Chevrolet will let Childress get away without putting up a good fight to keep them. It's a pretty big risk regardless of what Dodge may offer. There's no guarantee of anything. If the money and support is there I'm sure Childress will consider, but I'll believe it when I see it.
It's true that RCR has struggled and may be looking for a change to help performance, but I don't think it's Chevrolet that is holding them back.