Stark was written out of the series near the end of the third season so Paul Goddard could pursue theatrical acting. It wasn't the writers choice, but the actors. And he was still brought back to the series several times in season four, when his schedule permitted.
I figured it was something like that. Just like Virginia Hey had to leave because of acting concerns/not wanting to be bald/makeup problems (it was one or all of those), and Tammy Morrisson also left to pursue a film career, IIRC.
Had Goddard signed up to return as a regular for season five, out of curiosity?
And didn't Stark at least get a throw-away line at the end of season one explaining his absence? Or am I remembering a different throw-away line explaining another one of his absences?
Nope. He just vanishes. He does
get a throwaway line explaining what happened when he comes back in season two - he's returning the pod the Moyans lent him to leave last time - though where he went, who knows! Well, right, he was busy most of this time setting up the ingenious
plan for the S2 finale arc, but bear with me.
He doesn't get any such lines for his return at the end of S4, though, so you're probably thinking of the line I referenced.