It makes sense to bring back extinct species, to have the technological capability to do so, to get some practice in, but something that's been dead so long the

It makes sense to bring back extinct species, to have the technological capability to do so, to get some practice in, but something that's been dead so long the environment in which it flourished has since adapted, that's what I don't get. Should we bring back every single species that has ever gone extinct? Or only every one that existed while humans are in the fossil record? What I think it comes down to is humans don't handle change well, but trying to make the earth stand still is a fools errand.