Answer:
→To answer this question , let me start from here, I was sitting inside or under a Cuboid room or cubical room, having all faces either in the shape of square or rectangle, as every square is a rectangle.
→Why not circle , or any other Polygon was set as a tiles on the faces,or the building in which you are residing , may be you have seen the floors of room or on the roads where tiles are clustered, or the bricks, they are in the shape of rectangles, because these shapes provide stability , better assistance, Robustness, than any other shapes.
→Being a four sided polygon ,Between two edges , right angle is formed ,as well as when you draw a diagonal , two right triangle is formed, as right angle triangle is considered most sensible and substantial geometrical shape than any other triangular shape.
→When you will look at the universe most of the shapes are spherical , which are made up of concentric circles, when you observe things on earth most of the shapes are in the form of Squares or rectangles because they are well built that is most Suitable as well as most balanced for Humans,either in decoration purpose ,or for their dwelling place.
In Simple words , Rectangle which is most suitable for humans, Represents , Balanced, Soberness, And Robustness, that every human want in their life.