alt Hacker NewsPretty sure if you let only a handful of individuals from an almost-extinct species roam around freely in an uncontrolled environment, chances are pretty high something is going to kill them off before they reproduce, hence why they are almost-extinct.
The zoo provides a controlled environment needed to restore the species.
EDIT: typo/word ordering
Also, careful breeding to retain as much genetic diversity as possible is important to avoid collapse in small populations. Even if small local pockets survive, if each pocket is only able to inbreed with itself that will cause problems.
Our local children's museum is part of a network of sites working to restore red wolf [1] populations. Every few years they get new wolves as the coordinators move young wolves around to optimize mating pairs.
[1] https://en.wikipedia.org/wiki/Red_wolf