Not all positions in baseball are equal, because some require greater defensive skill than others. As a result, the offensive demands of each position are different. This is baked into those fancy advanced metrics like Wins Above Replacement, which credits catchers, shortstops, and center fielders for playing difficult positions.
At the other end of the spectrum is first base. Since the first baseman is anchored to first base, they very rarely need to cover large swaths of ground and very rarely need to throw the ball. Ultimately, this means that anybody can play first base, and therefore first basemen must be able to hit the baseball and do it well.