Genre is a style or category of music, art or literature that represents what the viewer is about to watch / listen to.

Genre is based around similarities and differences and should be predictable and expected.

Genre is important for the institutions who produce the work and the audience who consume it.

Quote : saddled with conventions and stereotypes, formulas and
clichés and all of these limitations were codified in specific genres. This was the very foundation of the studio system and audiences love genre pictures . . . – Scorcese, A personal Journey through American Cinema (1995)

Industries such as Warner Brothers or MGM make repetitive films or similar films due to a high investment in a singular genre. For example, a company would pay billions in props, costumes and co workers to be able to film a singular genre of film.