Movies typically strive for enough success to garner a sequel, many even branching out into expansive franchises, with spin-offs and TV adaptations. However, many of these film series, successful as they may be, would have been better off had they ended as perfect trilogies. It isn't always that later entries are bad, but turning a perfect trilogy into a much less acclaimed franchise can be a mistake. It also makes audiences see subsequent sequels as nothing more than shameless cash grabs.
Source：https://www.cbr.com/franchises-ended-as-a-trilogy/
