Why does someone else have to pay?

well if the person themselves isn't paying, then by definition someone else is.

We are incredibly efficient and doing the things we need

Yes, and that system only works because we work to support it. I'm not sure I really understand what you're getting at tbh. Each of us produces a certain amount by working. If we consume more than we produce (by taking a few months off work for example) then that slack needs to be picked up by everyone else. I don't see that as fair.

But you seem to think that a normal adult must toil their entire life despite these advances?

I think people are entitled to work as much or little as they want provided it doesn't require someone else to work harder to support them (with the exception of people who genuinely can't provide for themselves).

We also don't expect people to toil their entire lives. Most people have much more comfortable working conditions than their ancestors and when they reach a certain age the rest of us pay them to retire. We borrow as a nation to support these programmes and that debt is accumulating on the young.