Honest answer: to get to orbit, you've got to go really fast (like Mach 25) and there's a lot of air between you and outer space. Air resistance goes up as the cube of velocity, so you want to minimize frontal area. Balloons or propellers can't get you up to the necessary speed; you've got to use rocket engines. For aerodynamic stability reasons, those need to go at the other end of the vehicle; they also require lots and lots of fuel, and the aerodynamically best place to put that fuel is in a long cylinder behind the nose and atop the engines. The nose of a rocket is shaped the way it is because of a trade-off between aerodynamic drag at slow speeds through thick air near the ground and very high speeds through thin air higher up. The reason some rockets have a thicker section near the tip is because it turns out to be aerodynamically permissible to make the forward section fat, yielding more space for a physically larger payload while keeping the design of the engines and fuel tank section unchanged. Rockets with lots of weight up front are dynamically stable, too.
Why do space rockets and rockets in general always so closely resemble penises?