Think about the number of civilizations over the last hundred thousand years or so. Most of them are gone and we know very little about them. There are probably a lot that we don't even know existed in the first place. Ignoring the state of the world today, just on the numbers it's likely that this civilization will die and fade like every other.
Given the choice, would you rather your civilization be understood to people in the future, or would you leave as little as possible behind and leave future historians with only guesses?
> we should try to not vanish
If this civilization survives for the next few thousand years, the work of the preservationists will end up in a museum to early Earth civilization. If not, then the preserved work will end up in a museum to early Earth civilization, but run by aliens or something.
The need to be remembered is more of a philosophical argument, but I think it's just part of the human condition. It's why we pass our names to our children, why we tell stories. Thousands of years after the fact, almost everyone on the planet knows the names of at least some of the great conquerors of antiquity. Just about anyone you meet could probably tell you at least one story about Alexander the Great, or Genghis Khan, or Julius Caesar.
As a wildly successful civilization, the need to be remembered for that success is strong. Maybe just for vanity, but maybe future generations can learn from our stories as well. If our civilization does fall and we are not remembered, what happens next? Would we have another Dark Age? If the remnants of our civilization can still use the knowledge we've accumulated, would that help them rebuild?
It's really an unknowable question. The only thing we can be sure about is that it costs us relatively very, very little to preserve our records. If that effort is wasted, then so be it, but not putting in the effort would probably be bad in almost all situations, depending on your perspective.