Have you considered that server-side validation isn't being rigorously processed due to efficiency and performance reasons?
It slows down iteration, and the server's performance is already a concern. Validating everything server-side is a great way to introduce more bugs and slow the pace down.
This was the case in legacy, as well. It's not that they don't know how, it's that there are other priorities first, because it'll get a lot more complex once they start aggressively defending Rust from hackers.
There are efficient ways and inefficient ways to check for speedhacks. Do you really think I didn't think this through? Do you not see where I mention that I make servers/client applications? I'm not some random idiot. Like I said this method will only fix melee speedhacks. It wont have any difference on the speed that the servers run that you would notice.
Edit: Anyways, thanks for the help everybody. I got what I needed.