Waiting has a price. Money not spent on a long project can sit in a short Treasury, at a yield you can look up, or it can sit in a deposit account at a bank's rate. The yield is the published compensation for waiting. It is also the hurdle a risky project has to clear in the mind of whoever is allocating the cash.
That hurdle is not a scientific constant. Different firms use different ones, and most do not publish the worksheet. What can be said is that when the published long yield is higher, the hurdle that is tied to it is higher, and late cash flows have to be larger to justify themselves.