Source: I had a bunch of long conversations with FB Ads engineers about what they optimise for. I believe that it's a weighted sum over conversions, which seems like a better metric for an ads system (FB could increase profit in the short term by implementing price floors, but this wouldn't lead to more long term revenue, because advertisers would stop using the platform).
It does optimize for profit, just with extra steps. For most FB ads products (that you see in feed), advertisers pay based on conversions (views, clicks, likes, joins, purchases, etc.). So revenue is directly tied to conversions. Then there are extra steps weighing in revenue != profit, advertiser retention, repetitiveness, long term user value, etc.
Source: I had a bunch of long conversations with FB Ads engineers about what they optimise for. I believe that it's a weighted sum over conversions, which seems like a better metric for an ads system (FB could increase profit in the short term by implementing price floors, but this wouldn't lead to more long term revenue, because advertisers would stop using the platform).