Is there a particular reason that this forum doesn't use the "goes to top of page when posted on" mechanic that's used in many other popular forums?

Because (as far as I know) the back-end software doesn't support it, and implementing it is developer time. It would probably be easier to have an additional box on the right that points to the most recent post of each of "open_thread", "quotes", "media_thread" etc. tags.

(ETA: I've submitted an feature request)