Refrigerator/Amazon as in keeping people home a lot more?
I love the idea of exploration and frontiers, I will say. I spend a lot of time in exotic locales and places Westerners find uncomfortable. However it's also true any easily accessible 'true' frontiers are gone. Like you say though, this is part of a cyclical process.
In the time of Rome, all the frontiers were peopled over. But then civilization collapsed, bands of raiders swept the countryside, cities and towns were sacked and abandoned, and entire swaths of country became frontier again. In the time of the American settlement, again, you'd had a North America previously fully settled by Natives, but European disease swept through and killed off 90%+ of the population. Those who remained most likely consolidated into smaller and more spread-out communities, creating a new, largely empty frontier to explore.
And I agree too, as land fills up, jobs grow scarcer, and opportunities decline, people respond to these environmental pressures by reducing their reproduction -- which we're seeing. In all developed nations, all populations (including those recently transplanted from fecund third world states) adjust to sub-replacement-level reproduction within a generation or two. A lot of the people I talk to from cities are in their 30s or 40s and childless with no intention or desire to have families. They have a bunch of reasons why... but I suspect the main underlying ones are financial and logistical. Plummeting reproduction by city dwellers is a continual bugbear of urban societies, stretching back thousands of years (the ancients did all sorts of things to try to get their apathetic, hedonistic city dwellers to reproduce -- usually to no avail).
I don't think it's worth fighting these forces at a societal scale.
However, when it comes to the individual reader of this site, I am speaking to a man, not a society.
And for that man, an understanding of the forces that direct him, and a waking up to the fact that he is responding and reacting, rather than charting his own course, may be what he needs to allow him to free himself from the social and environmental constraints of his society, and plot his own way forward.