Hi NiteOwl - in order to join the curve ends need to be at least 0.005 units apart, and your curves here have ends that are much further apart than that, something like 0.18 units.

But the trick for your case here is that you won't be able to visually see the difference by only looking in the top view, because the curves are great in that orientation - they are on different z levels, you can see that if you switch to the Front view.

So if you drag one curve in the front view you can get it on to the same level as the other one with an "int" snap and then it will join ok after that. You can also squish them both down by grabbing the corner of the edit frame and squishing that down, that can be a good way to fully guarantee that everything is all on the same plane.

- Michael