well, virizion is an interesting case for this, but i'll lay things out.
virizion has the dual typing of grass/fighting, giving it a handful of weaknesses.
being commonly used as an offensive pokemon, dual STAB automatically is thrown in first.
( so for physical sets where you might would see x-scissor, you would be starting a bit like this )
STAB moves --- leaf blade and sacred sword / close combat
so then you have 2 slots for coverage or support.
well, while x-scissor may cover psychic types. STONE EDGE covers flying types ( 4X weakness ) and covers fire types ( regular weakness )
and then the last slot is commonly used for a supporting move, such as swords dance, work up ( mixed sets ) or even some times roar.
so x-scissor is normally blown back to the site, due to there being better options available.
it being a coverage move, gets outclassed by stone edge.
and that's pretty much it. hope that cleared things up a bit.