Thanks to a deal in place until 2025, Harry Potter is off all streaming services.
After many years of marathons on cable television, then being available on HBO and NBC properties, the film franchise is no longer available on any streaming service. The good news is, the cable binge watching is still going to happen.
The reason the films keep disappearing from streaming services after a month or two on is because NBCUniversal has the contract. The contract says the Harry Potter movies must be run alongside the "Fantastic Beasts."
Source:AV Club