Wouldn't it be better for the animals if conservation efforts were concentrated in the animals' native countries - in their own habitat? Less stressful, same climate & geography.
Yes, but not always practical.

But, then you wouldn't get the punters bringing their kids on a Saturday, would you? Education?
These punters are bringing a lot of money into zoos which goes towards the funding of research and conservation projects in the animal's native countries.

I also want to add I spent many a day at London Zoo as a kid, and it was educational for me and developed an awareness for animals and conservation that stays with me to this day.

I think the modern ideal of zoos as conservation centres is excellent, but unfortunately most zoos do not meet this ideal.

I also think there is an argument to be made that zoos are often underfunded and need to compromise their ethics to keep running.