Try submitting this paragraph as your next grant application!
It is actually possible to make educated guesses as to what's interesting and what isn't. It is just very hard.
The management of the old Xerox PARC, for example, was very good at it. So were the people at DARPA - about 40 years ago. So, once, was Bell Labs. And so on.
Needless to say, the actual process of guesswork has nothing in common with the modern scientific budget process.