Or just because, as these things go.
Just as Doctor Who fans across the years make a claim for ‘their era’ of Doctor Who and ‘their’ Doctor, so it is with another immortal character who has been portrayed and reinvented many, many times down through the years, Sherlock Holmes.
During this otherwise fallow period the Tour Brain Trust has been going through the immaculately produced Granada series of Sherlock Holmes true-to-period adaptations from the 1980s which starred Jeremy Brett, whom the Tour claims as ‘our’ Holmes. In the Series 3 story ‘The Musgrave Ritual’ who should show up but none other than Ian Marter, good ol’ Harry Sullivan as Inspector Fereday. It was a small scene insofar as the police presence in the story was almost purely perfunctory, still it was nice to see Marter again.
At a time in Classic Who where companions stayed for multiple seasons, and, yes we know that Marter was technically a companion for more than one season [a further digression–Terror of the Zygons was supposed to be a Season 12 story and in The Android Invasion, even as Harry Sullivan, he was just a guest actor like any other UNIT member], Marter is a little too easy to overlook.
Add to that it’s worth remembering that by some definition a ‘safety’ companion, cast even before Tom Baker was cast in the event the fourth Doctor was older so that Marter handle more of the physical action which in turn meant Marter was a one and done essentially.
Marter’s appearance in ‘The Musgrave Ritual’ was his last acting credit. The episode aired in 1986, and he died later that year aged 42. Too damn young.