Apple needed to show developers that Carbon should be a real and valid progress, not just a temporary stop, so they committed to using Carbon for Mac OS X Finder. The carbon version of the Finder was introduced in Mac OS X Developer Preview 2, before Aqua was revealed; It acted a bit more like NeXT, because it had a single File Viewer that had a toolbar and column view, but secondary windows didn't. At this stage, Apple didn't really know what to do with the system-overview toolbars it had inherited from NEXTSTEP.
It had taken Apple four years to find the new "Mac like", and this is the Mac OS X template that has followed the page. Here we are eighteen years later, and all the elements of the Mac OS X user interface are still recognizable today. So much of what we think of the Mac experience today came from NEXTSTEP, not Mac OS at all. AppKit, toolbars, Services, tooltips, multi-column table overview, font and color picks, idea of Dock, application packages, installation packages, a home folder, multiple users. You can even be hard pressed to find a Carbon app in your Applications folder today (and Apple has announced that they won't even run in the next version of MacOS).
Fascinating read by Steve Troughton-Smith about how Apple passed from NeXTSTEP to Mac OS X between 1
Apple will face a similar transition soon with the launch of UIKIT on Mac; Unlike others, I don't think it means a complete rejection of anything "Mac-like" stands for today. As I see it, it means that the idea of "Mac like" will gradually evolve into a state that feels comfortable and obvious. I'm excited to see the first steps in this new phase in a couple of weeks.