And even at top Legend, the winrate doesn’t justify. Ramp Druid’s 49.6% winrate is top of Tier 3 there.
The way I make sense of this is what I call “lack of self awareness theory.” Generally speaking, when I look at humanity, I consider emotions to be a powerful mind-altering drug.
Everyone (especially in Legend, but generally speaking as well) starts using a decklist with the hope that it’s going to perform very well. They’re hyped for it. But hype is mostly an emotion, and it doesn’t work on a rational level without great self-discipline.
If a player is having fun playing a deck, they might not say they’re having fun (for instance, if their deck is frequently complained about). They might not even realize they’re having fun. But what will happen is that they’ll be blind to the evidence that their deck isn’t overpowered. It’ll continue to feel powerful, even if it’s not — or if the evidence of its badness is simply inescapable, they’ll continue to try it anyway and complain about other decks being better while refusing to switch to them. They might even put on the persona of a hater and complain about the deck here, even as they continue to play it. 
On the other hand, if they aren’t having fun playing a deck, they might not realize that either. But the mind works overtime to rationalize what the emotions say are the truth. They’ll find whatever excuse they can to give up on their deck and switch to another one. Again, maybe that involves posting a thread here. Why? They don’t want to admit the deck isn’t overpowered — see, they are too good at Hearthstone to even build a deck that isn’t overpowered — but they, um, just don’t want to put others through the misery of playing it. Oops, Freudian slip, I meant playing against it.
All of this is a result of Johnny disease. Johnnies, we are told, play to express themselves. They invest their identity in their deck selection. Investing your identity in, well, anything really, gives your subconscious carte blanche to direct your consciousness to rationalize anything and everything to defend that identity. You can’t hate yourself, so if you make something a part of yourself, you will never see it clearly.
Getting back to the current meta, I think the reason there’s so much complaining about Ramp Druid certainly isn’t that it’s overpowered, and I don’t really believe people are self-aware when they say they can’t stand playing against it. It’s very difficult to be not able to stand playing against a deck that loses most the time. But when a deck does cool things, people want to believe on an emotional that coolness translates into winrate performance. But it doesn’t always, and that’s just empirical reality.
That’s one of the reasons.
Another one, based off my personal corporate experience, is strategic based on how to get active player numbers high. See, there are two ways to do this. One is to retain active players. The other is to bring new players into the game, which means appealing to interested non-players.
If the focus is on retaining active players, you wouldn’t want to nerf popular decks. Because they’re popular. That’s a pretty clear indicator the playerbase likes playing them, whether they understand why they like to or not.
On the other hand, if your focus is new players, you want the game to look good to people who are looking it up. You want Tweets to say nice things and stop saying mean things. You want Twitch streamers to be happy with the latest balance changes, and those streamers in turn listen to the burnt out former players in their audience. You focus more on the talk around the game than the facts of the game, because new players will never experience the reality of the game unless they like what they hear first.
Now just mix in my “lack of self awareness” theory, zoom out from the individual level to the community level (mass hysteria), and what I’d predict is what we see: borderline random, hypocritical, arbitrary decisions.