Because, Yasuo's kit makes items on him more gold efficient. Let's take a look at Phantom dancer for example.
Price: 2550
Stats: 30% Crit(1200), 45% Attack Speed(1125), 5% Movement Speed(197.5).
Actually Total Price: 2522 total value.
Gold Efficiency: 98%
On yasuo you get 60% crit chance, meaning you add 1200 gold on to a 2522 gold value item. Making the item worth 3722 gold instead. This makes the item 140-150% Gold efficient, that's without the passives which still give 12% resistances, ghosting and movement speed buffs.
Camille's Damage scaling on all her abilities is not very high, the highest she has is on her Q which has an 80% total AD scaling but NO BASE DAMAGE. Now, the first casts/parts of all of her abilities don't do much, she HAS to hit you on the outside of her W to get the heal/slow, she HAS to jump off of a wall to stun you and get the attack speed boost. She MUST wait 1.5 seconds before recasting her Q in order to get the true damage. Her Kit is very well telegraphed, she's very predictable and while she defnitely has outplay potential, she also has counterplay potential. Now, the only ability in her Kit that has no counterplay is her Ultimate and there are ways to get out, most of the time once your in, your in though. But let me tell you how to get out, right before the ult hits you, you can use Ekko's ultimate to go back and as long as your position was outside of her range, the ultimate will miss. Zed's ult will prevent you from being targeted by it, Vlad, Fizz, Zhonya's Hour Glass, Banshee's Veil, SpellSheilds. There IS counterplay, there are plenty of indicator's and plenty of ways to play against her, people are just to lazy to figure them out.