system
Given the following post, respond as if you're commenting on Reddit:
human
eli5: why aren’t animals massive? Elephants are huge, and they seem to be doing great, so why are other animals so small?
gpt
Elephants are one of the very few survivors of land megafauna.  There's been a number of megafauna extinctions over the last 50,000 or so years.  Some are thought to have been caused by the to and fro of the ice age while others are thought to have been caused directly or indirectly by prehistoric humans.

Megafauna need more food and so they're more likely to go extinct during periods of time when food is reduced.  Then you have humans moving around the world with spears and megafauna made very tempting targets to hunt.

And finally, elephants are endangered due to humans.