It suits the art style better
In the lead-up to The Legend of Zelda: A Link Between Worlds, it appears as if Link is getting a bit of a makeover. When the 3DS title was announced, Nintendo showed off a Link that looked mature, similar to Adult Link in Ocarina of Time. The art Nintendo recently released (shown below) depicts Link in a more cartoonish manner with childlike proportions.
Even though he looks sort of dopey now, the change is probably for the best. It fits better with the game's art direction, and is more in line with A Link to the Past's visuals.
You've changed, Link... [Tiny Cartridge]