Because the expectation that companies police every single bit that crosses their network is completely unworkable. It's functionally impossible to tell a licensed stream from an unlicensed stream, the distinction isn't available to Cloudflare or any other networking provider it's in private contracts between the copyright owner and the streaming provider and there's a whole snarl of copyright exceptions.

To make the distinction the LaLiga would want they'd have to inspect every single packet, determine if this is a LaLiga game, determine if it's the current game, and determine if it's a licensed provider. There's a reason section 230 was created in the US.