because they fit the parameters defined in the regulations, of course. FIA hasn't failed, all the other teams did for not doing it too.
edit:
as posted earlier:
http://www.formula1.com/inside_f1/rules ... 8/fia.html
10.3.1 With the exception of minimal local changes of section for the passage of hydraulic brake lines, electrical wiring and wheel tethers or the attachment of flexures, rod ends and spherical bearings, the cross-sections of each member of every suspension component, when taken normal to a straight line between the inner and outer attachment points, must :
a) Intersect the straight line between the inner and outer attachment points.
b) Have a major axis no greater than 100mm.
c) Have an aspect ratio no greater than 3.5:1.
d) Have no dimension which exceeds 100mm.
The major axis will be defined as the largest axis of symmetry of any such cross-section. The length of the intersection of this axis with the cross-section must not be less than 95% of the maximum dimension of the section.