You know what, I was having exactly the same thought regarding the Fermi paradox. Why don't we see alien civilization? Because we expect them to be massively large scale, and they probably aren't.
If we look at ourselves and our future. The human race might probably survive for a long time, but probably not in its current population levels. If we want some growth in our standard of living, that means more energy consumed individually, which we can't achieve at a global level. That's the gap you are talking about. So probably the great great grandson of the richest of today will be spacefaring, while the great great grandson of today's poor (well, today's 90% of the population) will probably just don't exist or at a civilization level that's invisible from far away.