People have been registering domains since the 90s (yes, some domains were even registered in 80s). Many of these domains stayed dormant for years because the extent to which web sites could evolve were unknown, unforeseen. No one knew how powerful internet could become, or the potential that the WEB held inside.
As the web technologies and websites evolved, so did the usage of the internet. Then, people started to realise the value of domains (or domain names as some call) which are basically your unique addresses in this infinitely large digital world.
Companies built their web sites on .com domains mostly (which is short for commercial), search engines were born and eCommerce was the new internet thing. Suddenly, domains (domain names) were the most valuable thing you could have in this digital world.
I think of a domain as a piece of land in the real world. The better the spot, the more valuable the house you build on it. You could build an apartment on a land at the edge of some forgotten land in the middle of some desert, or you could build that apartment on the most precious spot on Manhattan. Which one do you think would be more valuable? The exact same apartment in the desert would be worthless to many people while the one in Manhattan would worth millions.
That is why I think domains are and will be the most precious digital assets you will ever have. Your precious lands in the digital world.