Concerning why The Mummy 4 has not happened yet, there are a few reasons. For one, The Mummy Returns and The Mummy: Tomb of the Dragon Emperor were not as well-received as the first movie. Both received harsher reviews and were made on higher budgets, meaning their middling box office hauls saw the film franchise stall somewhat. After The Mummy: The Tomb of the Dragon Emperor received a 13% critical rating on Rotten Tomatoes and grossed $400 million worldwide against a $145 million budget, Universal Pictures decided to reboot the Mummy franchise.
In 2017, The Mummy was released, a reboot starring Tom Cruise that was set to kickstart Universal’s so-called Dark Universe franchise. The Mummy was just as big a critical and commercial failure as Tomb of the Dragon Emperor, essentially ending the franchise and explaining the lack of The Mummy 4. Similarly, the hiatus in Brendan Fraser’s career brought about by physical injuries and mental health problems stemming from his sexual assault allegation against Philip Berk saw The Mummy 4 become an unlikely prospect