To maintain a current you need to "push" the charge through any obstacles on the path.
If there is resistance against the current, then the "push" must be large enough to overcome this. The potential difference is this "push". Of course, as soon as the resistor has been passed, then a large "push" is no longer needed to make the current keep moving. Now what is needed is only a "push" to move through the remaining resistances of the path. So the potential difference drops and is lower.
See the picture in this other answer: Could someone intuitively explain to me Ohm's law? It makes it pretty intuitive.
If you are in doubt when considering electric circuits, think of it as a flow of water in pipes.
- The current is the flow of water,
- a resistance can be a narrow part of the pipe, and
- the potential difference (voltage) is the pressure (there is a potential difference, if the pressures are different at either side of some "resistance".)
