People didn't trade as much in Paleolithic times, so then they couldn't get a variety of resources. Because they couldn't get a variety of resources they then couldn't have better tools and weapons to defend themselves.
Now we trade for items like obsidian so that now we can make stronger, more powerful weapons and tools.
Now that we trade for items and materials we can make the area around us more beautiful and it would let us be able to create stronger tools and weapons.
Trading allowed us to make use of more resources and brought us into contact with people from faraway places.
Contacting other people also helped us know more stuff and share our knowledge with other people.