Ex-FB here. My guess is that it's primarily a combination of two factors:
1) Someone / some org was slow to notice that this was happening.
2) Bureaucratic muck slowed resolution down. Even once escalated, there would be a lot of red tape to go through to make the necessary changes to how things are ranked. The people noticing the problem most likely aren't the people able to make changes, the changes would need to be tested at scale and their effects evaluated, and the people making the changes would have a lot of deliberating, politicking, explaining, and appeasing to do. Add onto that that everyone is stressed out of their minds, worried about performance reviews, and having to balance changes they want to make against how they and everyone else are evaluated at perf time...
Ok, but all that must also be true for the change that originally created this situation. There's all this red tape and large-scale testing and then... nobody actually looks at what hits the #1 spot?
Presumably there are people who are in charge of designing the ranking algorithm, so they would look at the #1 spot, but they would also look have to look at numbers 2 through 1 billion, and evaluate over long timescales and have a lot of reports, and compare how one algorithm performs vs another one.
Maybe they've already evaluated and decided that they're ok with #1 being off, if the majority of everything else performs better. Doesn't really make any difference per se what is #1. And then even if you want to stop X becoming #1, you'll never truly understand the myriad of butterfly chain events that caused us to get here, and how do you know even if you've solved this one issues, you haven't just ruined everything else.
Remember spam is an adversarial relationship. Almost certainly when whatever ranking change was exploited here was deployed the top ranked items were great, then some actor started realizing what was being selected for and exploited it
> Even once escalated, there would be a lot of red tape to go through to make the necessary changes to how things are ranked.
When I write a program that accidentally gradually fills a disk with garbage, I don't wait until I can redesign the program before I delete the garbage.
1) Someone / some org was slow to notice that this was happening. 2) Bureaucratic muck slowed resolution down. Even once escalated, there would be a lot of red tape to go through to make the necessary changes to how things are ranked. The people noticing the problem most likely aren't the people able to make changes, the changes would need to be tested at scale and their effects evaluated, and the people making the changes would have a lot of deliberating, politicking, explaining, and appeasing to do. Add onto that that everyone is stressed out of their minds, worried about performance reviews, and having to balance changes they want to make against how they and everyone else are evaluated at perf time...