The Collins Dictionary defines freight as an uncountable noun meaning "the movement of goods by lorries, trains, ships, or aeroplanes."
This page on a US website is quite helpful discussing the use of the term "freight" vs "cargo" - note how many times the word "goods" is used in that discussion.
https://thejunctionllc.com/why-is-it-called-freight/
Broadly, I think "freight" implies goods that are being transported, in the same way that "mail" implies letters that are being transported. You could have a warehouse full of goods, but it wouldn't make sense to refer to them as "freight" if they weren't being transported anywhere.
Noting the comment about the LMS, I have a 1966 "Freight Handbook" from British Rail London Midland Region. The use of the term "freight" appears to be standard (there is a picture captioned "Lancaster Freight Terminal" - not goods depot - showing the handling of loose packages in various sizes from traditional 2-axle vans undercover in a large shed. However, there is long list of "Goods Agents" and a reference to a labelling service which "
at a reasonable cost" can be used for Goods stored with British Railways / Goods collected from a trader / Goods sent "to order" at destination station / Goods stored in public warehouses. The term "general merchandise" is also used.
There's a previous thread on this topic, although I don't think it reached a definitive conclusion.
https://www.railforums.co.uk/thread...-the-latter-become-the-most-prominent.213210/
It wouldn't surprise me if the later preference for the term freight was down to some change in "approved terminology" at some point. For example, when did goods yards and goods depots become freight terminals? It may be that the term freight was preferred to give a modern ring to the railways commercial offerings, or to bring it into line with the terminology in other modes of transport. That might also explain why they weren't bothered about terminology such as "goods lines" which would only be used internally.