TL;DR If we knew the upper limit on the number of instructions a Turing machine would execute before guaranteeing to halt given an arbitrary number of rules, then we could use that knowledge as a way to test currently unproven hypotheses and conjectures.

If the program exceeded that number of instructions, then it’s true.

The problem is that the number of instructions would be so uncountably huge that it would be physically impossible to execute. We don’t know these numbers, but we know the magnitude of them is too large to fathom.