Because the critic develops their own opinion on what they read from IMDB and even if they only ever learnt from IMDB and nothing else it's their own take on it. LLMs don't have their own take on anything - it's a statistical amalgamation of everything they read but they don't have their own personal identity or opininion. Likewise, providing a paid service website that only has one data source means you are just selling that data back without permission.