Why? Because the ability to measure isn't that precise. Even if the measurement is as close as 500,000 years, it might as well be an eternity. Because in reality that is what 500,00, a million, 65,000,000 years are.
It makes a huge difference to our concept of reality, the history of the Earth, and our place in the universe.
Things seem pretty stable to us, and we think things may well continue on as they have for a few more thousand years; but the lesson of the dinosaurs is that something can happen that will wipe it all away!
Maybe knowing that our time on this planet has been rather short in comparison to how long the Earth has been here will give us some much needed humility.
You may well think it doesn’t make any difference in your life, but for those of us who are intellectually curious and seek answers......
Beats squatting in a cave waiting for the other guy to tame fire.