I don't get shiv as yasuo

It's the same thing I build. Of course, I'm unranked, so what do I know?

Yasuo gets really strong burst, mixed damage and poke(hit a minion to bounce shiv proc to enemy) from shiv. These are all really good to snowball in the early-mid game. Phantom Dancer has higher DPS and makes you a much better carry later. This is the same on all champions pretty much and it is up to you to decide if it is worth it for that game. Most likely, it would be optimal to change your build depending on how each game is going rather than sticking to the exact same items every time.

He was nerfed when IE was. his passive doubles his crit chance, so IE and shiv gave him 90%, now 80. With yasuo, you're pretty much counting on your crits at that point; one fail in a fight is fine, but two and your damage is tanking.

Now with PD, you're technically "wasting" your crit chance, but getting to max chance (I don't think you can have 100) is where you need to be, and you've done it in two items still. You lose the procs which worked well with his mobility style, and the PD passive is a bit superfluous on him due to his dash, but you need top tier crit or you won't likely do as well, so your build is likely better than swapping shiv for PD.

Now I don't play yasuo, but if I did, I'd kinda miss the shiv builds, because getting a real early avarice blade on him can speed the rest of his build up, particularly if you find yourself steamrolling anyway and can skip shiv while you build the IE and keep the free gold flowing.