It's interesting how audiences have already become wise to movies that try to force the wider shared-universe stuff at the expense of providing an enjoyable complete experience in its own right (which seems to be one of the main recurring criticisms of The Mummy).
When Marvel first hinted at the shared-universe MCU stuff, it was a post-credits tag on a movie that stood in its own right and (crucially) was very entertaining and enjoyable, and left people wanting more. That was what really set up the MCU movies for success, rather than the shared-universe elements in and of themselves. (As Marvel found out with the misstep that was Iron Man 2, where those elements overwhelmed the main story.)
I think people are very attuned to this stuff, especially these days with so many shared-universe movies on the cards. It sounds like The Mummy hasn't succeeded in making the kind of film that people want to see more of, which is surely the primary goal.