because
adc doesn't typically scale well with hp items, budget hp items are definitely going to screw them hard but yes they can build it, it just isn't worth it unless the support is an asshole who doesn't build sightstone
Jungler sometimes gets it but not always. Even when they do they don't always have time to ward everything and it has less charges. A lot of times you just get this because support is an asshole who wont get sightstone
Mid could build this but mid needs to carry the midgame in a lot of cases and wont synergize well with the sightstone. Normally mid will only get this if they need defense and support is one of those assholes who wont build sightstone
Top can scale ok with budget building but a lot of times top's optimal positioning will not allow effective use of it unless top just doesn't do tops job kindof like how the asshole support who won't build sightstone refuses to do theirs.