Call_me_jorge said: "I thought Warner Bros didn’t have any stake in Harry Potter"
From the website: "HARRY POTTER CHARACTERS, NAMES AND RELATED INDICIA ARE TRADEMARKS OF AND © WARNER BROS. ENT. ALL"
From an article about Warner's involvement with Cursed Child:
"As crowds pack into the Lyric Theater in New York City to ogle at a grown-up Harry Potter travel through time in the Broadway play Harry Potter and the Cursed Child, there are several backstage characters who presumably wish that they, too, could go back into the past and rewrite history.
Those would be executives at Warner Bros. and its parent company TimeWarner. For while the studio owns most of the entertainment rights to Harry Potter and its spin-off series Fantastic Beasts and Where to Find Them–including films, live-action television, video games, theme park attractions–J.K. Rowling, Harry Potter’s creator, controls everything else. That includes the stage rights to her works, which means that, although Warner Bros. is a partner on Cursed Child, which is currently the hottest play on Broadway, the studio is not a lead producer or the primary stakeholder. In other words, Cursed Child is a Rowling production (along with producers Colin Callender and Sonia Freeman)."
TLDR, WB gets money from it but not as much as they'd like. Reading between the lines, it seems that they're trying to have as much brand unity as possible in the post-AT&T merger.