The arrangement of the atoms for shapes with only bonding pairs isn't directly based on the maximum bond angles between each atom, but on having equal spacing between each atom. If you visualize the 3d shape made by connecting the outside atoms, the shape it forms has edges that are of equal length and faces that are the same polygon. Here in Trigonal Bypyramidal, you see that the "faces" of the polyhedron are all equilateral triangles.
So while the bond angle may not be all the same, the overall molecule is arranged so that the atoms are of maximum equal spacing from each other.