why some animals/plants are stronger but weaker animals/plants thrive

Some large and strong animals such as a wooly mammoth or a dinosaur have become extinct in today's world but other animals such as cockroaches and plants such as fungi and lived to survive the millions of years of natural disasters. In my opinion the reason to this baffling question is that bigger animals are more prone to get wounded during natural disasters such as the ice age in the case of the dinosaurs but smaller plants and animals can be missed by these things. Cockroaches are also a fascinating type of animal that can withstand a nuclear bomb so that is also a big factor.