I got the notification: "Your game request has been rejected. Reason: Connect social media to your account". That makes no sense. Why should I connect my social media to the account as I just want to add a valid game with speedrunners to this database. What should I do? To make I request, I've already been forced to commit an own speed run which I wanted to do later, but why am I now forced to connect my social media to this account, which has no relevance for the game?

You connect social media so that you are easier to reach in the case that you go offline / inactive or anyone has any inquiries that need to be directed your way. Just as a contact method

Because people need to be able to contact you when there are problems, there have been more than enough cases where the mod was inactive and noone could contact the mod because there weren't any social media accounts linked to the account. And a run is required to show that your actually interested in running the game as there shouldn't be any empty boards on here.

^

If you really want a board for your game, connect your social media and submit your request with a video. If you don't have an account on Twitter, Discord etc... create it. It takes few minutes.

Since these guys didn't mention it... It's because when you request the game, you become the one responsible for the leaderboard.