In my opinion, the high turnover is a very good thing - at least early on.
Early on, you won't have a complete genome and probably won't have access to all of the genes and skins for a given dinosaur. So the first Cera you produce is probably at 50% complete genome, standard skin, no gene upgrades; and really just SUPPOSED to be replaced in all respects. You're supposed to build your park on an initial stock of dinosaurs, and use their paddocks for either superior successors OR something else entirely. And in addition, you're supposed to be exhibiting more than one dinosaur per paddock. I normally have three Ceras in a Paddock at any given time, and in the early game there will basically be two or three generations of them: One that dies early, one that lives fairly long due to a more complete genome, and one that has more complete genome and a new skin (with maybe a life extension trait if I unlocked it by then). The latter two end up living pretty long since they have a better genome, but really lifespan is a bit random overall - and that's not a bad thing at all. Quite advantageous, really.
I've had, wait... HAVE, cause he ain't dead yet... a 50% genome T-Rex that was supposed to die at 55 and is currently pushing 80. 'Expected lifespan' is an estimation of the average, and that doesn't mean everything will die instantly when the clock strikes that number. Some assets will outlive the average life expectancy, and some will die before it. Most die within ten digits of that number. But overall, as you complete genomes and add lifespan improving genes, you'll start to get big Sauropods with average life expectancy of 200 or more. I really don't understand anyone who complains about lifespans, at all. All the information is right there in the dinosaur stats. It's not a mystery why a dinosaur with only half a genome and a life expectancy of 55 dies at 57. How do you want it to be improved? All dinosaurs live to 100 and above? Time passes slower? What exactly has Frontier not done? They've practically spelled it out in big bold letters, right there in the genome editing menu. Is this 'lifespan too short' complaint some sort of ploy to get Frontier to add in dino reproduction? If it's the last reason, by all means continue, but let's drop the pretense and get down to what we really want Frontier to do about it. And if it's not about that last thing, then maybe it's you who are not playing the game correctly. As easy as this game is, you can actually make mistakes in it; mostly by ignoring the information the game provides you.