Has to? Why? No one would ever defend the statement that “all processes make us happy”…
"The struggle itself toward the heights is enough to fill a man's heart. One must imagine Sisyphus happy."
are the final lines of Camus' essay
One "must" imagine Camus was wrong. There are plenty of struggles humans do not find happy, particularly when they seem pointless or don't get you anywhere.
"God remains dead. And we have killed him. How shall we comfort ourselves, the murderers of all murderers?"
"Push this boulder, and imagine yourself happy."
How does this relate to art and fulfillment exactly?