The reason is because you are claiming to be an entity on the internet without any proof or verification that you are the content creator, i.e. assemblit.net. This verification is for completely different purposes and is not necessary (in my opinion) if someone who wants to be anonymous on here but writes unique content and doesn't post it anywhere else.

You'll find more people (including me!) will upvote your content that you are re-pasting here if you provide some type of proof. If you have control of your website, then adding a link to your Steemit account is a simple matter (as is contacting your web dev, if that's who needs to add it).