The problem with this is that you are biased in talking about how good gold/10 items are on carries. If you spend your first 900 gold on a philo and health potions for a carry, and I spend mine on 2 dorans, you are making a bet with me. You are saying "I think that you won't be able to deny or kill me in lane for long enough that this will pay out. The problem is that in 30 seconds (the time between minion waves), you only get 15 gold, meaning that if I can get just one caster minion per wave more than you, I'm actually not afraid to let you sit back and use that philo. Especially since it doesn't help your trading at all (though it lets you regen from trades faster, you are taking 20 damage per autoattack more, and I have 160 hp on you, meaning chances are I can just go all in and kill you while surviving. It also doens't help that buying a philo sets you 400 back, while a doran's blade only sets you 238 back from your first big item.
As it plays out in high elo matches (at least those on stream/in tourneys), the priority in getting gold /10 items goes as follows:
Support, Jungler, Mid (I guess going 3 gold/10 in mid is a new strat some people are using, especially on mids with good farming), Top (if they are gonna build a yomuu's or randuins anyways). AD carries never get them-- as far as I can tell because they don't want to make that bet with the enemy's lane.