PIE lacks the vocabulary for certain modern things like writing.

That's the best part!

Modern languages already have words for things like a mouse, a screen or the Big Bang, but it's all stupid stuff like an analogy to how a computer mouse looks like an animal because of its long cord-tail, a reference to the white screen a projector casts it's projection on, or a vulgar put-down of a theory being like God's orgasm.

If we take a dead language and start adding in vocabulary, we can quietly sweep that all under a rug before we encounter any alien species we have to explain ourselves to.

Alien species: "So you remodeled your language, removing all traces of history and culture from it, because you were worried about the impression you'd make on aliens you didn't know, you didn't even know existed?"

"You're the most pathetic people in the known universe."

I mean, we'll try, but we can only do so much. Even in ancient languages, every word for "tool" is also slang for "penis", and twenty percent of the verbs can also be used to refer to a sex act.