cuz the plot wasn't heady enough
and the close-ups and cuts in Leone's films were rhythmic devices to elevate tension.
They were also reaction shots.
You had a pretty good feel for who's who in those flicks due to plot, so they were not revealing the craggy topography of anyone's soul.
Also, WTF at ^^^THAT^^^ horseshit.
Tarantino took the technique with none of the theory behind it.
He does that a LOT, and waits for critics to make up shit like above to give more weight than what's actually there.