I don't think one aspect has been specifically mentioned although hinted at.
In the days (now long ago) when I was directly involved, many private freight terminals - particularly stone depots - had restrictions on their times of operation, laid down by the local authority. This was presumably because of considerations about noise and associated road traffic, and I don't think such restrictions will have been eased with the passage of time.
I would suggest, from hazy memory, that these restrictions would be likely to include a complete ban on weekend working.
As an aside, the M-F window was often quite limited and, if such restrictions applied at each end of the transit, and the latter was of more than about 6 hours, trains could only run in a very limited time band. It is perhaps not always seen by railway passengers that their requirement to arrive at destination reasonably near to a particular time may also apply to freight traffic.