When you sort by newest games, many aren't out yet. Can I request a game request a game that has been announced? I mod Crossy Road and want to request Crossy Road+. It seems to have a story mode.
Unless it's a big release or has a demo that fits the rest of the rules, the site doesn't add games before release.
@TRLittleToaster I'd like to agree but I can't. Go look at the games page and sort by newest. Look at the kind of games that are in there. NBA2k where the main category is playing a game, an indie shooter game, a bunch of early access games... Also, I've never seen a game not even have categories: https://www.speedrun.com/heart_lock_a_free_metroid_inspired_game
From the Game request rules: Well-known users or moderators of other games in a series may request unreleased games beginning 21 days prior to launch. In rare cases, requests for unreleased games may be accepted by well-known users and only at site staff discretion. Series moderators may also add games to complete a series. Games will not be added prior to release for users who are not well-known.
So as a mod of another game in the series you definitely have a chance (but no guarantee) to get it accepted before release.
Edit: Also keep in mind that in some cases series mods still exist that can add games to their series without going through the support hub requests (for that new Sonic game for example that may have happened)