I don't know the technical reasons behind it; however, it is tied to making sure that invalid requests are not treated as valid. Using a deeplink is technically an invalid request that has unexpected success in connecting (unless changes were made and i have missed it, which is possible) as that URL does not exist on the system but is being caught up in the PTP hostname. The HTTP URL is validated fully for where to send the redirect against; since it doesn't exist, it gives a 404.