In message , J Clavox
writes

I was wondering this myself but maybe Ashford isn't geared up to
handling E Terminating and departing from there.

Even if it is possible, there would have been difficulties getting
passengers into or out of London from Ashford, as the fire also
disrupted southeastern services between Ashford and Victoria (I think
they were diverted to Blackfriars). Although there are other
possibilities, I suspect that services in south London were so badly
disrupted by the 24-hour closure that trying to get the large numbers
carried by Eurostar through the mess was just impossible.

--
Paul Terry