If the rumor is true that Sommers had total control of this movie, then everyone who signed off on that should be fired. So The Mummy being a surprise hit caused his stock to rise, but then to follow it up with The Mummy Returns and Van Helsing? Did no one notice his escalating problems?
Despite weak critical response, The Mummy Returns was actually more profitable than its predecessor. And although Van Helsing wasn't quite as profitable (nor well received by critics) as Sommers' previous two films, it still made 300,000,000--nearly twice its budget--and certainly grossed more in ancillary sales (television, DVD, etc.). Even The Scorpion King, which he scripted and produced, was a modest financial success.
In short, Sommers' creative success or failure means little to studio heads who see that his films have grossed a lot of money in the United States and abroad.