The biggest problem for Lethal Weapon 5 is, unfortunately, its most famous actor. The first Lethal Weapon movie was the debut of screenwriter Shane Black, who would go on to write and direct films such as Kiss Kiss Bang Bang and Iron Man 3. Starring Mel Gibson and Danny Glover as a pair of mismatched cops investigating a murderous conspiracy linked to an illegal drug-smuggling ring, Lethal Weapon opened in March 1987 and became a massive hit, grossing over $120 million worldwide. This level of success meant that a sequel was inevitable. Lethal Weapon 2 was released two years later and made over $100 million more than the first movie, cementing the franchise's status.

https://screenrant.com/lethal-weapon-5-mel-gibson-star-problem/