We don’t need to have everything explained by the film. There are other non-film sources with which to draw on for relevant information to people who would care.
TFA as a film doesn’t explicitly explain how the Starkiller Base weapon works or why the explosion could be seen from outside Maz Kanata’s castle. The novel does. ROTJ doesn’t explain how Leia obtained a costume impersonating Boushh; or why Lando, the droids, Leia and Luke arrived at Jabba’s Palace separately.