I am wondering why there is no IL leaderboards. Is there a particular reason or are they just not added lol
If you want to submit to IL boards, you can submit to https://www.soniccenter.org/ . Have fun. (Edit: It's because there's almost no IL video competition for this game and as a result there's no real reason to just have a bunch of empty IL boards here, so just go submit to TSC instead.)
I noticed that there is no individual stages leaderboard on the website. I just saw your message about the Sonic Center website, but idk, I like the speedrun.com website since it is easy to see the runners strategies. I am only number 17 in the Casino Night Act 2 ingame leaderboard, so I wanted to improve by looking for new strategies. Unfortunately, on the Sonic Center the best time for this stage is 39.55, while mine is 39.19, so I think they do not have much to add. I really think adding the individual stages would create some competition, and the cost of doing this would be close to none.