It's a feature for developers, because it's in the code, and it doesn't break their product. It won't affect anyone but users like you and I that are developers themselves, it might break their code, but that's not Twitter's responsibility.
Non-deterministic class names are quickly becoming the norm for a lot of good reasons.
> Twitter now has obfuscated CSS classes for everything
Non-deterministic class names have been popular for a while, especially in React; open up Chrome inspector on a Gmail tab. Sometimes they are used for minification. This might not be a (strictly) hostile change.
It annoys me too, I write custom CSS for any site I use a lot.
Non-deterministic class names are quickly becoming the norm for a lot of good reasons.