The "Layers->Delete->Selected Layers" (2023) and the "Layers->Delete" (2024) tools have been designed to prevent undesired deletion, so when you delete a layer its contents will be moved to Default Layer and then the selected layer will be removed. If you want to delete a layer and all its contents, you have to select the layer, to select "Layers->Pick Objects" (this will deselect everything and will select all and only the contents in that layer), to "delete active", and lastly you can delete the layer itself. Of course, if you have any invisible entity in the layer, you have to turn it visible otherwise it cannot be selected.
It seems a long process, but it takes more time to explain it than to do it.
Hope this helps.