I didn't like the switch to a single pilot position, but i know it was just to save money from hiring somebody with no lines to play navigator.
But that was already done on TNG, it has nothing to do with Voyager specifically.
Tom is the navigator. If you recall, data was the ships operations officer (that was what his station was devoted to. A position which worf held briefly)
They just moved the operations position to the rear of the bridge.