It’s all about the tone. Moving the position of pickups can be a great way to alter the sound your guitar produces. So much so that brands and manufacturers factor this into their designs and require their pickups to be installed at an angle. Generally speaking this difference in sound manifests itself in such a way that pickups positioned closer to the bridge will sound warmer and pickups placed closer to the neck will sound brighter. Angling them gives players the option to utilize both.