The reliance on "reboots and established franchises" over "creativity" or original ideas has a lot to do with the collapse of the "blockbuster movie renting" and private DVD and Blu-ray owning secondary revenue streams.
It used to be the case where a movie could "fail" in the "box office" but later gather profit or "not lose money" via these other revenue streams. Nowadays, studios, on average, can only make the bulk of their revenue in the "box office".
Movies, on average, last 1 to 2 months in theaters. This is very little time for enough of the public to determine a reasonable consensus on what's a "good movie", on average. Meaning, "creative original films" easily "tank" in the "box office" not because they're "bad", but simply because they're new and unknown and not enough people got a chance to see them.
"Reboots and established franchises", on the other hand, already have audiences or fans, and since people, on average, human nature, prefer to spend on something that has historically provided a good experience instead of risking it, then it makes perfect sense that studios favor investing in films that have a better chance of gathering enough audiences for the "better box office" results.