Occam's razor specifies that "entities must not be multiplied beyond
necessity." Materialism cannot be true, despite it's seeming simplicity. Therefore one must multiply the entities until one can arrive at a true, simple explanation with the fewest number of extant entities.
The mind is not a physical thing, despite it being connected with and informed by the brain. Consciousness and the body cannot be separated, because consciousness is not physical and thus no separation can take place. Consciousness 'winks out' when the mind is anesthetized. This is not possible for a physical object but eminently possible for an non-physical (abstract) one. Physical objects are subject to state change, while abstract entities exist, well, differently. It may involve state change, but it also may simply be there/not there.
Abstract things can still exist, when you learn things, it is an abstract thing, the mind, interacting with other abstract things, learnings. These abstract things interact with the physical world through the instrument that evolved to allow them to do so, the human body and mind.
There's another example I can use. When we model a system using state machines, the diagrams of those machines provide a representation of the workings of the model. We can point, on the state diagram, what the underlying system running the state machine is doing. But that 'pointing' isn't the actual system, it's an abstract thing that helps our minds understand the underlying system it's running on.
Did you catch the invocation of the law of parsimony in the last paragraph? The very existence and usefulness of Ockham's Razor invalidates materialism. Entities are not physical objects.