I have had the same question come to my mind often too, the only way I can rationalize it is to say I think 'the whole of creation groans' and 'by sin death entered the world (kosmos)' are two different things-the latter a subset of the former. I think the meaning of 'kosmos' may be pivotal- 'God so loved the world ('kosmos'). I do not think God so loved plants and insects that he gave his Son but I think he so loved the 'sea of unsaved souls' is what kosmos is referring to A spiritual realm reference.. Likewise by sin death entered this 'sea of unsaved souls'. Do plants and insects and our individual cells die? i define death as the spirit leaving the body, so, then it can only experienced by 'nephesh chayyah' creatures which plants, insects and our cellular components are not?.