Apple needed to show developers that Carbon was going to be a real and valid way forward, not just a temporary stopgap, so they committed to using Carbon for the Mac OS X Finder. The Carbon version of Finder was introduced in Mac OS X Developer Preview 2, before Aqua was revealed; it acted a bit more like NeXT's, in that it had a single root window (File Viewer) that had a toolbar and the column view, but secondary windows did not. At this stage, Apple didn't quite know what to do with the systemwide toolbars it had inherited from NEXTSTEP.
It had taken Apple four years to find the new 'Mac-like', and this is the template Mac OS X has followed ever since. Here we are, eighteen years later, and all of the elements of the Mac OS X UI 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 views, font & color pickers, the idea of the Dock, application bundles, installer packages, a Home folder, multiple users; you might 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 on how Apple transitioned from NeXTSTEP to Mac OS X between 1997 and 2001. The purpose of this analysis, of course, isn't to simply reminisce about the NeXT acquisition but to provide historical context around the meaning of "Mac-like" by remembering what Apple did when the concept of "Mac-like" had to be (re)created from scratch.
Apple is going to be facing a similar transition soon with the launch of UIKit on the Mac; unlike others, I do not believe it means a complete repudiation of whatever "Mac-like" stands for today. The way I see it, it means the idea of "Mac-like" will gradually evolve until it reaches a state that feels comfortable and obvious. I'm excited to see the first steps of this new phase in a couple of weeks.