Why can those living species survive today in their native ecosystems but the extinct species cannot survive in the los angels today

In historic times, the land was incredibly different from what it is today. The species living in a certain area today have adapted to the modern day while extinct animals would not be able to adjust very well due to the sheer amount of changes that have been made. For example, If they were a predator and used tall bushes to hid in, they would starve because there are no bushes to keep them hidden in order to hunt. Vice versa if they were a prey. The ecosystem just doesn't support certain types of animals anymore because the ecosystem evolved without the extinct species.