Recognize those are the average cost, during a boom time. It includes going after marginal areas of the plays that won’t be pursued with lower prices.
For an example, say a company has 10 areas where they were considering investing for new oil production. Break even cost for them are: 51, 53, 55, 57, 59, 61, 63, 65, 67, 69 $/bbl. Their average break even costs are $60/bbl.
If they just shelve the top 5 most expensive projects, they just lowered their break-even cost to $55/bbl. No technology change, but still lower average cost. They will just produce less until prices climb up.
Now combine that with less demand for equipment, material and labor as the drilling programs get scaled back. The producers cost for new production then fall even lower.