The thing is, many of the authors of KotOR and TSL mods are difficult to reach, and it's thus very difficult to gain permission to post them to the Nexus. Robin and the staff over there are pretty strict about posting "stolen" files without permission, even when due credit is given.
But for those who can be reached, I think their mods should definitely be posted to the Nexus.
Been a NEXUS fan for quite awhile, and it makes managing them super simple. Not to mention the gaming communities(s) are flocking there now that they've opened up the "mods for ANY game" upload wizard.