Is it logical for BF to post a thumbnail ONLY when you have uploaded an image and not when you link to one? No.
Is it logical not to give the writer the option of how large an image to display? No.
Is it logical to force the reader to click on the image to see it full size? No. (Besides, how many people actually do that, or know to do that?)
But that's only a minor quibble. Now that I know how it works, I will post images to a URL somewhere instead of uploading them.