Because we only live a short while, we don't take a long view and there's a soft cap on society's accumulated wisdom. (In a smaller scale it's like companies losing "institutional knowledge" when employees leave.) People would act differently if they knew they'd be around for 700y instead of 70.
> That's what we thought would happen [with the Internet], but look at what we actually did
You're not seriously suggesting humanity is better without the Internet…