I know this thread is a year old but I really need to talk about this atm.
Because they're those champions that are seen doing those amazing plays/highlights or whatever, and of course they always try to replicate. Yasuo mains I can respect a bit because of the much higher skill curve and difficulty to master compared to others, but Yi is such a linear champion so them getting salty at other teammates tends to piss me off.
Just now I had a game with a Yi main (I knew he was a Yi main because he was mastery 7) that started the first 10 minutes normally but then started flaming everyone because of "ks-ing", saying that he did the most damage and we were all simply walking in to take his kills. What pisses me off the most about this guy was that a) he did not do the most damage, I did, and b) considering that he had 11 assists while I had 19 and the rest of my team had 12 or 13 meant that he was likely the one ks-ing more. He even threatened to afk, saying, and I quote, "you'll lose without me", even when the game was 30 minutes in, we had taken an inhib, and I was 19/8/19 as Eve jungle while Diana mid was 17/12/14. After the game the graphs showed that I did the most damage but the Yi kept flaming, saying "oh it's because you ks'ed and bought items".
At that point I was like "what in hell's name was this guy trying to say? If I ks'ed him a lot, wouldn't I not have as many assists as I did, and wouldn't Yi have more assists than just 11 out of the 68-kill game our team had? And as for items, OF COURSE THAT'S WHAT YOU DO. IT'S HOW YOU WIN THE GAME! Even then, I did not achieve my full build as Eve that game. Yi did. Hmmmmmmmmmmmm and at the end he said "good luck in bronze". I checked his account, and he's bronze 2. Ironic, ain't it [slayer-jinx-wink] . On my NA account I'm silver 1 but since I live in Jordan I have the EUNE account for smurfing and fun with friends.
I can't really understand why players like these are so damn salty. I swear on my life the amount of flaming I've gotten from these guys have overshadowed every other champion I've played against. Sure, there are other champions that love to flame people (Zed, Talon, Riven, Garen, Lulu, etc.) but Yi mains take the cake. Every time I see a Yi main with mastery 6 or 7 on him I automatically feel the urge to mute them because they'll flame me to hell.
Every champion is a good champion. (Except Aatrox tbh, even with his rework.) But a lot have a much easier skill curve. Ashe, Yi, and Garen, for example. Hell, when I was first playing League, Yi jungle was my thing. I would play that to hell. Why? Easy. REALLY, easy. And especially from seeing videos from like seasons 4 or 5 when AP Yi was the most broken champion and if you didn't get three pentas and solo baron in a game as Yi, you were considered bad. That's why I don't like Yi all that much. Yasuo? High skill ceiling. Zed? High skill ceiling. Riven? Barely played with or against her. But Yi? Oh ho ho. Linear, easy, and quite strong.
Some Yi/Yas/Zed mains would go "oh we get salty because our teams don't help us in teamfights", which is a totally valid reason. However, that does not change the fact that most of these mains (Yi and Zed in particular) always think they can 1v5 while half the team is respawning, and when they die they flame people by saying "report xxxx no help and feed". Believe me, no one likes to see your balls of steel when you jump in for that pentakill with your salt seeping through your screen.
If you're a Yi main and you get pissed at other people for not giving you any glory, then STOP PLAYING YI and pick up a less linear champion. Again, Yasuo is great, but he's god hard to master. People will respect you more than if you were playing what is considered the easiest champion in the game.
Sorry for the massive rant. That game I had that I explained earlier seriously pissed me off. Such a massive shit talker, and flaming our adc for using their ult on a minion wave. Here's a nice little message for each Yi main out there. Nobody likes salt. And nobody likes a 12 year-old Yi main with mastery 7 who flames everyone for not giving him a pentakill every game. Nobody cares how godly you are at Yi because a toddler can pick him up and play well. If you want to get glory, play a real champion please.
TL;DR - To answer your question: Yas mains because he has high expectations from everyone and a good Yasuo main is hard to counter, thus leading to taunting and flaming everyone. Yi mains because he's such a linear and easy champion that makes the game feel so much easier for players that they get a god complex whenever they're playing him.