Asymmetry
Why do people say "Thank God!" (i.e., Thank you, God) when something exceptionally good happens (that is, a strong desire is satisfied), but not "F___ G__!" (i.e., F___ you, G__) when something terrible happens?
A theist might answer that God has a plan, which we only dimly comprehend but comprehend to be good (in the very nature of the god we believe in). So when something that we can immediately comprehend as good happens, we thank God for it; but when something that seems bad happens, we reserve judgment because we assume that, somehow or other, it is all for the best.
To this I think an apt response comes from the story of the Taoist horsetrader:
One day a horse belonging to a Chinese horsetrader escaped from the corral and ran off. The horsetrader’s neighbors came by and offered their condolences for his bad luck.
“Why do you say it was bad luck?” asked the horsetrader.
A few weeks later the horse returned … followed by a band of wild horses, which the horsetrader promptly corralled.
The horsetrader’s neighbors came by and congratulated him on his good luck.
“Why do you say it was good luck?” asked the horsetrader.
Now with so many horses, the horsetrader and his son were busy taming them. One day the son was riding a particularly spirited horse when he was thrown and broke his leg. After that he could only hobble around.
The horsetrader’s neighbors came by and offered their condolences for his bad luck.
“Why do you say it was bad luck?” asked the horsetrader.
About a year later a troop of the emperor’s cavalry galloped into town and demanded that all young males be drafted into their ranks and go off with them to fight in the latest border war. Everyone’s sons were taken except for this one horsetrader’s because of his handicap.
The horsetrader’s neighbors, although dejected, came by and congratulated him on his good luck.
“Why do you say it was good luck?” asked the horsetrader.
-- from memory from an unremembered source
So I don’t buy the plan answer to my question. Meanwhile my atheist friend Mitchell Silver came up with a marvelous answer, to wit:
Answer: sycophancy. I say "thank you, officer" after every acceptable interaction with a police officer. I never say "f___ you, officer" after an unsatisfactory interaction.
Thus, on this understanding, it is fear of God’s power rather than love of God’s goodness that motivates our preference to thank but not curse God.