My guess is that they did it because client side pos data means much less stress on server as well as a more fluid experience for the player (no stutter stepping in ff). Likely more attributed to the former, as they could still fix the issue by filtering the client data on the server but that, again, would lead to stress. Whether that should be a realistic issue is another story. It's like SE made this amazing game and bottlenecked it because for some reason they wanted to host the thing on a bunch of toasters.
SE has made it apparent that they outright refuse to hire GMs for any issue. Instead they are taking up (imo overly) ambitious projects such as the misguided chat filter and the abomination that is rmtpwner.
"Why did you ban thousands of accounts?"
"Because RMTpwner banned them."
"How do you know RMTpwner works?"
"Because it banned thousands of accounts."
