Is it that hard to buy a sightstone?

Why do some ap supports refuse to buy sightstone in low elo?I was playing a ranked match last night and i got frustrated that our support lux refused to buy sightstone.Now usually i dont mind this if an ap support is actually doing something but this dude/girl wasnt even building dmg items and yet refused to buy sightstone.I was frustarted since its a low elo acc and i am the only person who bought pink ward.And i have noticed this a lot in low elo that some supports just refuse to buy sightstone and provide vision and its not limited to ap supports.So i guess i am kinda confused why dont they buy it?Should they even buy it?It frustrateing for me when they dont since riot removed stealth wards and low elo usually doesnt buy pinks :/ EDIT:After reading the comments apperently i am complete fucking moron for thinking that a support shoukd by it and i as a mid main should buy it if i need it or my team needs the support can then provide dmg.So no need for more comments and as someone who plays supp as secondary role i shall never buy sightstone again.Ty for educating me <3
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