Well, you're suggesting that they used vague language because they believed it was impossible to be more specific. I am suggesting that they used vague language for an additional purpose - because they wanted to expand the power of future decision makers to determine what is reasonable or unreasonable under the different circumstances in which the future decision makers would be living. I am suggesting that they knew that circumstances would change and that future decision makers would make better decisions than the drafters could make about what would be reasonable or unreasonable under those changed circumstances.
Does that disturb you?
They had already incorporated a solution into their work. It's called "the amendment process."
Does that disturb you?
It disturbs me somewhat that you think like this. No, it doesn't disturb me that the founders thought like this because I have no belief that they did.