Here's a bit of conspiracy theory on my part.

I just came across a post on the internet about the CBIP or " CME's Central Bank Incentive Program ".

Now I don't know how politically influenced the US Central Bank is but if that is the case, the Indices could be "tweaked" to the upside on a given administration to make the administration look better. Particularly if you can print your own money...
I cannot even vote in the US, hence I am no republican or democrat, BUT no wonder that as election day approaches a strong statement from one of the sides is "oh look how the previous administration left the Dow Jones and where we have it now."
And I say this because it seemed we are seeing some "failed crash" IMO or at least this artificially interrupted bear move (V bottom with a strange looking range aftewards).

In conclusion, it would be bad for any administration to get a "Bear year" during elections year, right?
Maybe sustain it within a range would help the party...
Furthermore, is this free-markets at its best?

Below the links:

https://www.zerohedge.com/news/2014-08-30/its-settled-central-banks-trade-sp500-futures

https://www.cmegroup.com/international/emea/international-incentive-programs.html

So there it is open for discussion for the more politically-oriented posters.

I would imagine that central banks would be more attracted to using GC (gold) and 6E (euro/dollar) or any other currency
future, or interest rate future, rather than a pure equity future play.

Futures could be a way to hedge operations.
For example if a central bank wants to unload or load Gold or foreign currencies.