Folks are confusing Facebook (the product) with Facebook (the company).
Facebook (the product) is an absolute dumpster fire that is primarily used to spread propaganda that Facebook (the company) is unable and unwilling to stop.
Facebook (the company) is doing just fine, because they quickly realized social media sites are basically dating sites, where each new age cohort attaches to a different one. That means Facebook (the product) can indeed be awful and not affect the company much since all the users just moved to Instagram.
A better analogy would be Pizza Hut or Taco Bell ... They absolutely market both and some share space, that doesn't mean they each respectively don't care where the spend goes. If people are buying from Taco Bell, the Pizza Hut a block away may or may not shut down, and spending efforts will reflect those differences.
My analogy would be that Yum Brands doesn't care whether you visit Taco Bell or Pizza Hut. In the same way Facebook (inc) doesn't care whether you visit Facebook or Instagram.
But, the marketers hired specifically for Facebook do care if you're going to Instagram more since it endangers[1] their product... Facebook Inc cares because one of it's branches is less worth in investing in but is happy the money you're spending is still within their product universe.
I think that you're being a bit over simplistic, there is a lot of decision making based around company component performance, poor sales number within the Facebook native platform may influence more money being redirected to support Instagram which might end up as a personnel cut in an extreme circumstance.
I have an interesting approach. Maybe it falls flat on its face, but maybe it could work.
Create a "liberally themed" Facebook clone and onboard a bunch of people during the run up to the election. Give them tooling under the guise of campaigning, but also get them to use Facebook like features.
Ban any conservative thought or commentary. It's harsh, it's undemocratic, but it plays into the attack. Especially if you can drum up press coverage on Fox News.
Hypothetically, a polarized platform could create a stir. Maybe liberals on Facebook get interested. Maybe it leads to a small migration. This furthers the right-leaning polarizarion of Facebook's userbase, causing more liberals to flee. Thermal runaway.
This "Facebook is for Republicans" narrative is aided by the recent rumors that Zuckerburg has been meeting with Republican leaders about campaign advertising.
If you completely brain drain Facebook of the liberal demographic and make it skew far right, are the engineers, predominantly liberals, going to continue to be excited coming to work to build that product?
I think it's an interesting approach. It's far-fetched and kind of sneaky, but I'd love to see something like this attempted.
It would prove a new vector of attack for entering the social space. Something that even Instagram might be vulnerable to.
Because the audiences are different?