They're just not great at civilization, or rather their preferences are vastly different from Europeans or Asians. Even when handed advanced infrastructure built by basically aliens from space (Europeans) it just rots. No one cares enough to maintain the alien infrastructure once the alien invaders decide they were a bit mean to the locals and should go. Back to mud huts and charcoal fires like we've done for 10000s of years.
Look at anywhere in subsaharan Africa.
They're just not great at civilization, or rather their preferences are vastly different from Europeans or Asians. Even when handed advanced infrastructure built by basically aliens from space (Europeans) it just rots. No one cares enough to maintain the alien infrastructure once the alien invaders decide they were a bit mean to the locals and should go. Back to mud huts and charcoal fires like we've done for 10000s of years.