In some cases, the shape of the bullet is due to the design of the firearm. Tube magazine,centerfire rifles must use blunt bullets to prevent chain fire in the magazine.
Other cases involve the traditional type and twist of the rifling. A round nose bullet is shorter than a "pointy" bullet and will be accurate in a slower twist rate such as is standard in the 22lr for it's entire life.
Many more modern cartridges have gone through a transition from round nose to spitzer(pointy) during their life. Early military designs used round nose bullets. The 6.5x55,7x57,and 30/03(30/06) are examples of this among others. Their original designs used a heavy,long, round nose bullet but the design was capable of supporting the change to a lighter, shorter, pointed bullet.
This info is fairly general and jumps over much more specific points of this topic.