The site has been discontinued (but kept in limited read only form). As part of the migration to read-only, the media data was lost. See e.g. https://github.com/openai/gym/issues/718#issuecomment-329661594
It’s a bit sad that the more accessible and media-friendly public side of the community around OpenAI was dropped like that. Maybe there was more expectation that the community as a whole would run that side, but I know I want to play with RL instead - I’d like a site with videos and leaderboards, because it sounds fun and motivating, but I’m not going to make one.
However, the libraries like gym are still available, maintained and are great way to get started.
There are other options possible, such as https://www.riddles.io/competitions for 2-player game bots. That has leaderboards, re-plays of games etc.