Youtube is an intent-based ad platform. Meaning you only advertise to prospects who are actively searching for what you have to offer.
Facebook is a disruption-based ad platform. Meaning you're advertising to a huge pool of random prospects - regardless of whether or not they're interested in your offer.
Also, with Facebook you're paying every time someone even takes a glimpse at your ad, whereas with YouTube ads you only pay if someone watches 30 seconds or more of your ad.
This is why YouTube ads produce much higher quality leads than Facebook ads, which means YouTube produces a lot more profitability.