As a newer user that's actually one of the things I love about HN, that people accurately and succinctly summarise the link's content in the title. And if not, someone will ask them to do so in the comments.

Instead of "Thank You, GitHub", the post title should be "GitHub's CEO farewell address" or something.

That's actually (generally) the opposite of what happens. Usually someone will editorialize the title and the admins will change it to the contents of the title tag. If you see a good synopsis it's probably because the author of the piece took the time to write a hook-ful title.