Perhaps it was not prioritized because a certain amount of scale, in terms of active members, is required to be very successful (to the extent of getting to "rule the world" kind of level)? Many companies start with fewer user hostile items until they reach a massive scale so as to protect their turf from competitors who may use that against them as well as to keep people coming back to the platform often and for long durations.
Given that FB is now a public company, it needs to prove to shareholders, beyond anything else, that it's growing its revenues and profits. Turn FB into a company that puts its users first instead of its profits, and its stock price would probably be 1/3 of what it is today.
"Connecting the world!" is indeed the job of almost all employees at Facebook. You can have a large majority of the company focus on this one goal, and also know that the byproduct of that goal allows you to expand another part of a bigger goal: to make more money on ads.
A company in a capitalist economy must make money, of course. No one is arguing that and no one is saying that Facebook doesn't want - indeed must - make money.
It's like asking an Uber driver what is job is: "to transport people!". Of course, that much is obvious. If you ask someone in the "growth" department (or whatever) what their job is - the description will necessarily be much different.
But a repeated theme of the conversations was me trying to get inside their heads: I said: "Your job is to figure out when I'm going to be making a decision, purchase or whatever else, and make sure that your advertisers' message is in front of my eyes just as it's occurring to me to make a choice".
With creepy consistency, the replies were rejections of this idea. "No, we're connecting the world!".
My conclusion was an echo of the Upton Sinclair quote:
"It is difficult to get a man to understand something, when his salary depends upon his not understanding it!"
I hope that the quitting phenomenon is real, and that it represents the creme de la creme, with many other options, leaving because they can no longer avoid understanding. If this is happening, then FB's decline will just accelerate.