Why isn't the fit "perfect" if the continents were once part of pangea

It's been billions of years since Pangea brook apart. Think of all of the forces that have acted upon those continents since. Erosion from water is a big part. Islands have broken off; earthquakes have shifted continents; glaciers have formed, mountains have formed by continents being smashed together. It wasn't a clean cut. Imagine having week old birthday cake left overs. Already when it was fresh and you cut it, crumbs fell off and the cutting wasn't neat. Now a week later as you're trying to pick up an already cut piece, the frosting is falling off and taking pieces of cake with it and it's crumbling. It isn't a perfect fit because time has altered the shapes of the continents. 

Rnabothrnabothdnadnaboth