Well, the Traveler brought the "Golden Age/Powers(warlocks, hunters, and titans" or in this case "Freedom", now it has brought slavery or "The Darkness" and we are now limited to exploring the entire universe. And it's said the Black Garden is inside of the the Traveler which also has, you guessed it, the vex. Now the Traveler is weak, still, and "rotting".

Also, there is rumored to be more than ONE "traveler" and the universe

It's a very sound explanation but the traveler is not the answer