Fg=GMm/r^2.
If the distance would increase, that means that the gravitational force would decrease, and if the planet was able to break the original gravitational force and go to a higher orbit, what would bring it back into position again, since the gravitational force would be smaller at that point in time....
The same thing which causes a pendulum to swing back and forth, or something that is rolling up a hill due to its momentum to stop and come back down.
CONSERVATION OF ENERGY.
As it climbs up out of the gravitational potential well, it slows down.
Remember, the only thing keeping an object in a circular orbit is its sideways momentum, if it lost that (such as by slowing down), then it would start falling inwards.
If it goes to fast (such as by falling inwards and gaining speed) then it will fly out.
An elliptical orbit is basically just switching between them.
A more technical explanation:
Lets say it starts off low, but it is going to fast. This means that it will deviate from the circular orbit and start flying outwards.
This means the object it is being attracted towards is no longer off in a direction at right angles to its path. Instead, it is now slightly behind.
As it's speed is still too fast, the force of gravity falls further and further behind, slowing it down more and more.
It eventually reaches a point where the sideways component would be enough, but it is still ahead. This means gravity keeps on slowing it down.
But just after that the sideways force is too great. This means it starts falling back, and thus the force of gravity can now start catching up, so it starts going from slightly behind to beside.
Eventually it reaches a point where it is directly to the side, as gravity has now caught up. But now the object is going too slow for an orbit of that distance. That means it now starts falling inwards, and falling behind. That means the direction of the force of gravity now gets slightly in front. This results in it speeding up.
This continues until it reaches the point where it is travelling at the right speed for the sideways force, after which it is going slightly too fast and thus it starts catching back up with gravity falling behind and eventually ending up purely sideways and we are back to the start.
You said "No, we still have 2, it is just that only 1 has something (significant) in it."
Where is the second point and what is located in our solar system at that point!
For what?
The solar system doesn't just have one.
Did you mean for Earth?
If so, one is the barycentre of the Earth-sun system (as an approximation anyway).
As for the second one, well it would be 2 times the distance between the centre and the focus away from that.
The eccentricity is the distance between the centre and the focus divided by the semi-major axis.
That means the distance is the eccentricity times the semi-major axis.
For Earth, the eccentricity is 0.0167086 and the semi-major axis is 149.60 e+6 km.
So the distance from the focus to the centre is 149.60 e+6*0.0167086=~2.5e+6 km.
So that would be a short distance from the sun.