Why Nerf New strong picks and try to keep traditional Pick strong(OP)?

So I've watched my fair share of league videos, with the meta changing every week its nice to get a heads-up on the things that are changing, and I noticed something that tends to happen a lot. "So and So champion is looking good now with so and so build, so make sure to abuse it before it gets nerfed" Now i understand if this new build on a champ makes them actually op but a lot of the times it just brings them to relevancy. Right now Liss+aftershock is on the rise, and thank god because Lissandra has been on the weaker side of the meta and this might just bring her to relevancy. Is it OP? I don't think so, it just makes her a good pick. But watch them nerf her meanwhile Irelias fucken running around with High mobility, high burst+ sustain damage, utility and cc+ survivability and tankiness??????? I'm an irelia main and I just don't understand why whenever something new becomes strong they just nerf it to the ground so that traditional strong picks come back up? I'm not upset my favorite champion isn't meta womp womp, I'm annoyed that anytime some new is decent it gets nerfed, meanwhile, they allow actual OP champs to stay.