Mark Nottingham, chair of the IETF HTTP Working Group, wrote on his blog that Tim Bray brought this draft to the HTTP Working Group some time ago because Tim and many others thought that it was important to show online censorship because "the 403 status code says "Forbidden", but it doesn't say "I can't show you that for legal reasons." " This was pushed back.
Later, with the rise of online censorship, many sites began to adopt the code for experiment and more wanted to let people know that the content were blocked due to legal reasons. Among them was, Lumen, a database that collects and analyzes legal complaints and requests for removal of online materials and Article19, which works on behalf of freedom of expression. As a result, on Friday the 18th December 2015, the IESG approved publication of 451, the formal name for which is "An HTTP Status Code to Report Legal Obstacles".
"In some jurisdictions, I suspect that censorious governments will disallow the use of 451, to hide what they're doing. We can't stop that (of course), but if your government does that, it sends a strong message to you as a citizen about what their intent is. That's worth knowing about, I think." :concluded Mark Nottingham in his blog post