You do not want thrusters at the front because you might have something similar to the Coanda effect, where the flow of gasses will tend to stick to the surface of the material due to superficial tension. This means the surface of the ship is going to be constantly battered.

If you wanted, I guess you could go for a 'Hammerhead' design, where the thrusters are at the front, but placed at a certain distance from the fuselage. This however increases the construction costs and the overall mass of the craft.

Such designs do however present the advantage of having the motor force at the front, which creates a bit more stability. But the much larger cross-section and mass might offset this advantage