Why don't the present shapes of the continents fit perfectly into a super continent

There are several reasons due to which the present shapes of the continents will not fit perfectly into a super continent. The main reason can be attributed to erosion and rise and fall of the water levels. The edges of the continents have got eroded due to several natural causes and this has changed the shapes by a great margin. The water level of the seas and oceans keeps on rising and falling due to the tides. this never allows the continents to remain in the shape in which they were separated from one another. The shape of the continents are always changing and so it is never possible to fit them in the same way as it was before getting separated.