A lot of resource —> happiness.
A lot of resource —> energy for curiosity.
A lot of resource —> energy and time for high achievement at work.
So happiness is a correlate for staying in high-resource state in a stable manner, which correlates with high achievement, the quality employers seek.
Immediately one can consider a trap of unhappiness, similar to the trap of poverty: being worried makes you perform worse, which leads to problems with employers, which males you even more worried. Unlike poverty, this potentially could be countered by antidepressants.