Actually, it was Alan Moore who created the character, but Neil does insist on the "tyne" pronunciation, too.
(Sometimes, I also use the "teen" pronunciation, but it's either because I forget, or because I feel like giving up arguing about it.)
This reminds me of a time back in the day when I was in an on-line discussion of 2010, and happened to mention a scene in the movie where Roy Scheider and James McEachin are on a sidewalk bench with the White House in the background, discussing the issues at hand. Off to screen left, there's a...
Possibly for the same reasons that for the last 30+ years most people pronounce "John Constantine" as "Constan-TEEN" when it should be pronunced "Constan-TYNE" (according to the man who created the character).
Maybe. Or maybe there is some confusion by others on the matter.
Per the AFI Catalog: "According to NYT, Robert Louis Stevenson, the nephew of the author, appeared in the film as an extra, reportedly because he could speak with a cockney accent."