In "Unjustifiable Risk - The Story of British Climbing", Simon Thompson makes the argument that in short, climbing is a leisure pursuit, and that until the industrial revolution, people did not have time for leisure pursuits because getting by and scraping your way through life was extremely tough and time consuming.

We should not discount the idea that many a highlander could have been to the top of Ben Nevis over centuries without seeing any need to record the deed. But ultimately what Thompson is saying is, there was no need to climb the mountains so why bother when you spend all your waking hours making sure you have enough warmth and food to keep yourself and your family alive for another day, and you're not going to be finding shelter and sustenance at the top of these mountains.

Of course the aristocracy will have had plenty of free time to undertake such trivial pursuits but climbing mountains at that time wasn't considered an appropriate pastime for the aristocracy. Indeed, climbing in its infancy really began as a working class pursuit while the upper classes concerned themselves with more gentile pursuits such as hunting and polo.

One of the byproducts of the industrial revolution was time. Suddenly the middle classes (and less often the working classes) had more time on their hands thanks to growing wealth, and started coming up with activities to fill their leisure time with. Some people started climbing.

The lack of todays' technology and safety equipment meant that climbing didn't start out with people looking for the steepest, most difficult possible routes up mountains, quite the opposite. People began to look for the easiest routes up the highest mountains, all over the European Alps as much as back home in the UK. Summit bagging was all the rage during the "golden age" of alpinism where every mountain you could see was ripe for a first ascent and there was literally a "race to the top" of pretty well all alpine peaks.

The mode of climbing during this age was the antithesis of what we see today with "alpine style" aesthetic and ethics (meaning travelling light, mostly in a team of two, leaving no trace of your presence as you go). The wealthier middle classes would lay siege to the mountains, taking dozens of servants, pack animals, and huge amounts of food drink and alcohol to feed everyone. But I digress.

I would thoroughly recommend you grab yourself a copy of Simon Thompson's book if you want to learn more about this. Its a spectacular book, thoroughly researched and speaks from a UK perspective. In fact you can see why the industrial revolution and that fact it happened first in the UK, is the very reason for the fact that British people have lead the world in climbing of all styles the world over (until relatively recently - that last 50 years or so - when it has balanced out globally), which is why the British claimed most first ascents throughout the Alps in Europe, as well as beyond into the Himalaya and of course the first ascent of Everest (which was considered a British triumph at the time in the sense that New Zealand was part of the Empire at that time).

TLDR: The industrial revolution meant people had, for the first time in history, spare time. Some people used this spare time to undertake such frivolous and largely pointless pursuits as mountain climbing (pointless in the sense there were no tangible benefits - we don't need to wax lyrical here about the myriad of mind and body benefits to being outdoors and undertaking tough challenges).