Let's understand this with a rod.If you take a finite charged rod and assume it to be a bar magnet. If u know the magnetic field lines of a bar magnet, it is similar to the electric field lines of the charged rod(not exactly same because electric field lines are perpendicular to the rod along the body and curved at the poles).This curving of electric field lines at the poles is known as the fringing effect.

To understand this imagine a point charge anywhere in the middle of the rod(since it is a continuous linear distribution of charges),it will have charges on its either sides and since each of them have an electric field in similar fashion,the net effect of field lines come mutually perpendicular to the rod.

But if u imagine a point charge at the end points of the rod,it has a charge only on its one side and nothing on the other. So the repulsion comes from one side and it has freedom on the other. This makes the field lines to curve.

If u r able to understand this then u could easily imagine it for any continuous charge distribution (like sheet).

Also if the rod tends to infinite length then its end points tend to infinity and so fringing tends to zero.