In addition to what everyone else said: location and range safety. The launch sites they use were built for non-recoverable launch vehicles which are dropped t

In addition to what everyone else said: location and range safety. The launch sites they use were built for non-recoverable launch vehicles which are dropped to the sea. The launch sites have a narrow range eastwards, and SpaceX needs to adhere to the restrictions despite being able to land the boosters safely. This means that their rockets will inevitably be going over the sea.