There's a practical element to that, likely; Roger Carmel's likeness rights are notoriously unavailable. Off-hand, I remember the Star Trek: 25th Anniversary PC game only showed Mudd's face in shadow, and one of the John Byrne photocomics got around it by having Mudd somehow assume the form of Captain Kirk. The fact that they can just make Harry Mudd look like a totally different actor who is also Harry Mudd on-screen was probably seen as a far-superior solution to "recasting" him with a non-Carmel but Carmel-esque face.
Relatedly, while Jeffrey Hunter has appeared as Pike on several novels from Pocket (
Legacy and
Burning Dreams) and Marvel seems to have had likeness rights for
Early Voyages (though it's hard to tell with Patrick Zircher's art style), DC Comics did not, so when they used Pike he usually appeared with facial hair (a mustache in an annual drawn by Gordon Purcell, a full beard in another story set on Talos IV).
I don't know why they bothered, though, since the Batman '66 comic portrayed numerous other characters they didn't have likeness rights to, simply redesigning them (e.g. Chandell was blonde, Black Widow was much younger, etc.).
The
Batman 66 comic... Yeah. I'm probably going to misexplain this. Based on talking to people at DC,
Batman 66 was not a comic based on the Adam West
Batman series, which is why characters didn't always look the same or details line up (like, there was a London, not a Londinium, in the
Batman 66 comics). It was a
Batman comic in the
style of the Adam West
Batman series, much as
Batman Adventures was a
Batman comic in the style of
Batman: The Animated Series. (Though the crossovers --
Green Hornet,
The Man from UNCLE,
Steel & Peel, etc. -- really only make sense as being Adam West
Batman comics.) That's how I understood it, which is why I put together a Batgirl pitch with 66-ified versions of Azrael and Anarky, even though they're characters that debuted
long after Adam West's
Batman. I think they 66-ified easily -- Anarky fits well with an organization like the SDS, Jean-Paul would be a late-60s computer science guy at Gotham University.