You don't think the largest streaming platform on the planet wants to keep their intellectual property a secret? This isn't about being embarrassed over some comments, it's about completely revealing the algorithms that move streams to the promoted views, limitations of their filtering systems, the time it takes for someone to count as a 'viewer'... there are many pieces that are no longer secret and can now be manipulated by people trying to promote content or game the recommendation system or bypass filtering.

There is also the issue of security. I'm sure people will be combing through the source code to find anything they can exploit, even if it's a simple XSS attack. It could either be sold/used for malicious actions or submitted to the bug bounty program for the reward money.

Doubt they care too much about bad words in commit messages, what they should worry about is if they've ever checked in passwords/secrets/private keys and not re-written the git history

More things to keep an eye out for;

Snippets of open source code.

Commit messages that imply anti-competitive behaviour ("Committing a change to the API to lockout competitor XYZ").

Commit messages that imply code theft ("Using a method that we used at my previous company").

etc.

Sometimes things that look sketchy might be innocent but will still cause nightmares for twitch since they'll now have to play defensively as people call into question anything that ever went into the repo.

Of course they want to keep their source code private, like most software companies do. They consider it their "secret sauce", their prized IP.