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.
