It’s simple… harvesting more than the population you are hunting can sustain. A lot of animals outside or deer are regulated through a lottery system, if everyone who wanted to hunt a bear, mountain goat, or cougar did every year, we’d have none.
We have deer seasons for a reason. Lots of times you can only hunt the male bucks to keep populations in check. People have decimated populations. Look at the Goliath Grouper ban in Florida and how the species has recovered.