I think someone already said it once. But let me repeat it: Reaching the sun - or in this case the black hole - is HARD.
When you're on a planet, you are orbiting around the sun at quite a lot of speed.
Basically, to reach the center of the system, you need to counteract the entire velocity that the planet has in relation to the central object.
Otherwise all you're doing is raising, lowering or otherwise altering your orbit AROUND the sun.
Easiest way to get there would be to fly off the planet, accelerate in the opposite direction the planet was heading in (so decelerate in relative to the sun) and then just fall in once you're at 0.
But that is ridiculously outside of what you need to get out of a planet's atmosphere and into an orbit.
But then again, I don't know why you're really arguing about this in a movie that has anti-gravity drives in the end.