They CAN.
They usually don't.
First, most zoos end up having to be driven by capitalism (even if they are non-profit), and as such are incentivized to try to game-ify the experience. Many parents and most children don't want to pay money to be lectured to. They want to have FUN.
Therefore, the experience ends up arriving at an awkward intersection between science and commerce, and it can create unhelpful connotations between animal captivity and entertainment.
Second, most people have an inate understanding that a living creature in captivity is wrong, and likely not super beneficial for the creature. So the zoos - both super conservation-focused ones, and brutal cruel entertainment zones alike - have to make an effort to justify and convince the public that actually the animals are well taken care of, are comfortable, and happy, true or not.
This further perpetuates the idea in people's heads that animals exist for our amusement and we can give them a better happier life than the wilderness.
Why is all this a problem? Because childhood memories are formative and significant. These experiences shape us and our understanding of the world. We are in a significant time of species extinction - caused directly by human activity. The amount that people care about this, about deforestation, about habitat loss, directly affects how much they care about voting for policies that either help the situation, or exacerbate it.
I'll reiterate - I think zoos/aquariums CAN be a force of good here and help change many people's minds. But I don't know if overall they are a net good if the majority of the uneducated population just treats them as an entertainment escape and formulates in their head that it's not a big deal if rhinos go extinct as long as we can still see them at zoos.