The same reason the literal entirety of society exists. After we completely figured out food, water, and shelter, we got bored. We stopped being at risk of famine 10k years ago, we pretty quickly figured out fermentation and distillation makes water not kill us, and we figured out how to house everyone.

Then we kept just making that faster and easier to accomplish.

Well what do we do with all that free time? Fuck play games, do some entertainment, kill other people over petty nonsense, create pointless class based societies that generate artificial scarcity simply because a few people are greedy and most are too trusting of those greedy people, enrich out lives through momentary joy.

So in the dark ages of computing this tradition was continued and a very smart, highly paid scientist in charge of tens of millions of dollars of equipment made some of that equipment play table tennis.

A few decades and massive corporate funding of naive over enthusiastic nerds with much cheaper but more powerful equipment later and we have video games instead of going to the pub to play dice or doing a war…