Because cost of leases, equipment, drilling and labor were also ridiculously low by today's standards. The cost of doing business was low by today's standards, thus were retail prices.
“How did the “global economy” survive, when oil prices were low enough, that gasoline was 30 cents a gallon?”
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It survived because the dollar still had some value. A fast food lunch could be had for less than fifty cents. A new Mustang could be had for three thousand dollars or less. In my area ten thousand dollars would buy a brand new small brick house and lot. If you had a hundred dollar bill you could go on a vacation. I used to make a hundred and ten a week as a single man and I drove a new car and partied like a madman. Truly adjusted for inflation and with factors that are generally overlooked accounted for that was probably equal to fifteen hundred a week now.
In 1991, my employer took out a long-term lease on the Zapata Lexington, a semisubmersible rig rated (then) to 1500' water depth. This was before Zapata's sale/merger. At that time, we had that rig for $15,000/day, and they also offered us the sister rig Concord for similar money. There was a $1000/day difference because one rig had a Varco top drive drilling system and the other did not.
Those were depressed rates occasioned by the aforementioned depression in natural-born prices in 1990/91. Rates like that were barely enough to "keep the dog alive" and wouldn't even allow for a fresh coat of paint for the rig.
Now you couldn't sniff the diesel exhaust of a rig like that for that kind of money.
Although I should imagine that rates are coming down rapidly.... I should go look at Rigzone.com.