The idea is that you use the dinosaurs to bring in visitors/guests and than throw them in the grinder to regain half of the money you spent on them, which is necessary to outweigh the costs of the dinos, but you can stop doing it or at least do it less once you get the upgrade that increases their lifespans, though that will reduce your profit and you will still need to keep the carnivores fed by using herbivores or other carnivores (or visitors).
Buuuuttt... they're canonically made in a lab and die in a matter of seconds no matter what, so you're technically not cutting their lives that short.