(user hat on)
Like most of the users, it works just fine for me, I just drag them in a new file and be done with it.

No need to investigate if it inserts in LayOut or any other workaround.
(support hat on)
In my job as working for the distributor of SketchUp in the Benelux, I get to see many strange things. We do not have access to bug reports or have any insight in the code, they’re somewhere in the Denver area but we do have direct contact now and then. Most of the time, it is an existing problem that is easy to solve or not (yes, there are bugs in the software).
The difficult part is usually in trying to figure out what is different in the set up or workflow of the user that faces a problem.
I only read this thread when it already had passed to 90 posts or so, so my (professional) curiousity was triggered.
My thinking was this: the importer in SketchUp might not work, but perhaps the one that LayOut uses might. Maybe, a (prior) installed extension that messes with the SharedPreference.json file is corrupted somehow. Not sure if SharedPreferences.json are copied upon a new installation, but since LayOut doesn’t have live extensions, it should have a ‘clean’ one.
So I posted a quick question, easy to test, no messing around in ~/library etc.
Another user did try in LayOut and that triggered at least the bugsplat reporter with useful information for the developers. Probably, the importer in SketchUp catches the faulty import and just ignores it, while in LayOut, the program splats.
These bugreports are helpfull and there are two: One directly for Apple, the other one upon starting the next session of SketchUp or LayOut. These get sent to the developers.
So, I might ask another question about your specific setup that is easy to test:
Can you create two folders on the desktop, one called ‘MYFOLDER’ and the other called ‘myfolder’ ?
