Because of the rhetoric being used in the political arena. If "the 1%" almost entirely changes every year, well... what's the problem with that? You're always going to have a top 1%. Don't we want it to have a significant amount of turnover? Indeed, these numbers sound perhaps a bit low, if anything (is it really that unstable up there? That's not obviously good to me.). If it's not the same people all the time, it's not obviously useful to be talking about them as a distinct group.
Maybe it is useful. But it's something that goes from almost self-evident, to badly in need of being established.
On the other hand, the idea that a small handful of people have concentrated such vast wealth that they've disenfranchised the rest of us, a handful that is a great deal less than "the 1%", is actually a wildly more potent political story. Even this here libertarian type might be open to some significant actions taken to ensure that such concentrations of wealth are ameliorated, as a key part of my personal libertarianism is that monopoly busting is a key useful function of government, and I'd consider this to fit in, if it is true. It's still something that needs establishing, though, not mere assertion.
One has a hard time not imagining the .001% cackling with glee as the press focuses on "the 1%"; it still leaves them lost in crowd of millions, hardly singling them out for any treatment, while the 1% itself is peopled with a significant number of people who apparently worked their way up the ladder, however briefly that may have been. That doesn't sound like a good set of people to target, if there's no actual "institution" there.
And now, let me reiterate my first sentence; this is because of the political rhetoric being used. If it wasn't for that, this would be a relatively uninteresting question. But if it's going to become essentially part of the platform of one of the major parties, it's worth examining for truth value.
The evidence we have so far points to a higher churn rate the closer to the top you are. According to this [1], the top 1% had a churn rate of > 50% over a decade, while the top .01% had a churn rate of > 75% over the same period. The "Fortunate 400" mentioned by the article is something like the top .0001%, and had a churn rate of 99% over two decades.
I'd love to see deeper analysis though. What does the churn rate look like as a function of top percentile size? Do the choice of endpoint years matter significantly? Also, as you ask, what might be the optimal churn rate economically?
I agree, I would love to see more detailed analysis, as well as a fresh, open-minded investigation into the question of what optimal is without very, very large assumptions being made casually. (Perhaps such things exist. Links welcomed.)
Step one is always always always identify the problem. As I said, I'm open to the idea that there is something that should be done here, but it is absolutely vital that we first identify the problem carefully, before we start throwing around solutions to non-problems. This is... or at least SHOULD be... a non-ideological statement. We will all most assuredly disagree about what optimal should be, and what actions we should take, but we should all be arguing from the same basis of facts, and this sort of discussion strongly suggests we are not in the possession of the facts we thought we collectively were (and/or that we were told we were, and/or that we collectively just assumed without examining... I know I didn't ask these questions personally, so this is not intended as an attack on anyone else). This is not something to be glossed over casually on the way to espousing the same ideas we would have anyhow... it's a big problem that should be solved first.
> If "the 1%" almost entirely changes every year, well... what's the problem with that? You're always going to have a top 1%. Don't we want it to have a significant amount of turnover? Indeed, these numbers sound perhaps a bit low, if anything (is it really that unstable up there? That's not obviously good to me.). If it's not the same people all the time, it's not obviously useful to be talking about them as a distinct group.
If the people in the "pool" competing for each year's exorbitant profits (the 0.1%) remain the same every year, there may still be a problem. That pool is called "the 1%"
I'm kind of struggling to find the personal relevance of a story reporting churn within the top 1%.