Why do structures like the Eiffel tower have a tapering tip but a broad base?

As the effel tower being roughly perpendicular to the earth's surface,exerts an enormous perpendicular force (or pressure) on ground.For that reason when the base of eiffel tower is made broad,this enormous pressure gets spreads throughout a huge area and acts on a larger area

and hence it avoids the sinking of the tower.

as a general rule, scissors have blades less than 6 in (15 cm) long and usually have handles with finger holes of the same size. shears have blades scissors used to cut hair or fabric must be much sharper.