To maintain layers you would need to choose export as original in the LR Export dialog.
Thanks for your reply. I understand that I can preserve the layers by choose Original as the image format. My question is why do the TIFF and PSD formats flatten without warning? I won't go into how much time we wasted trying to discover why some folks lost the layers when exporting while others did not but it was a lot. Why does Adobe do that? It certainly is not intuitive. I can't think of any circumstance where I would want that behavior. At the very least the export dialog should offer a choice as to whether layers will be preserved. If this behavior is a WAD instead of a bug I would really like to understand the reasoning for the design.
I’m only another user like you and can’t comment on the design, but I guess it’s just intuitive to me because of the fact that LR does not have a built in layers capability.
Lightroom does not do layers.
When it reads a PSD or TIF file that contains layers, LR is only reading the full-size JPG preview in the file.
When LR exports a file as TIF or PSD, it is creating a new image from the user's edits. As such there are no layers to be exported.