If we want to describe it at the atomic level ...
Voltage is potential difference, which is directly proportional to the energy that each electron has as it jumps from one atom in the conductor to another. Because there is a small amount of heat generates in the jump, the electron leaving the atom has a very slightly lower energy level than the one that came in. Thus, over a long distance, you get voltage drop. The energy that each electron has also dictates the distance that the electron is capable of jumping.
Current is proportional to the number of electrons that are jumping (the technical term is "propagating"). Large numbers of electrons moving at once all generate heat that compounds and, if the conductor is not large enough, can cause the conductor to heat to unsafe levels.
A conductor that is carrying far more electrons than it was designed for will compound this heat rapidly and reach the melting point of the conductor - this phenomenon is used to advantage in fuses to protect everything, and used far too often to disadvantage by people trying to save money by installing cables that are not rated high enough for the task.
You can have a very large number of electrons jumping at the same time at low voltages (eg in an arc welder) or you can have a few electrons jumping a long distance (television tubes worked this way - high voltage, low current, shoot the electrons and manipulate a magnetic field to deflect the electron path from the cathode (where the electrons come out at the back of the tube) towards the screen.
Pop a spark plug lead one day and let it arc while the engine is turning over. There is a limited current and a limited voltage. As the lead moves further away from the body of the engine, the sparking stops - the potential difference (voltage) is not high enough to allow the electrons to flow.
Thus you have the reason for voltage drop over distance and the need for cabling that is good enough for the task.
Just as an aside, the voltage drop is the reason why we don't have power lines on 240V. The big lines can be 32,000V and a substation will bring that down to 11,000V, 415V and 240V for delivery or redistribution. The 11,000V lines will enter a transformer mounted on a telegraph pole and be reduced to 240V for household use.
Clear as mud?