Sourdough bread is one of the oldest types of bread in existence that was consumed in ancient Egypt and Greece. It stuck around for centuries in Europe, and after French immigrants brought it to the city, it was a popular choice during the Gold Rush in San Francisco. From there it spread to Alaska and Canada. To cut a long story short, by the mid-20th century, mass-produced bread was taking off, leaving little room for sourdough. But now it's back.
So while you can make sourdough starter at home using flour and water, it is a bit of a process. It can take nearly a week to properly prepare, and you need to be careful about all those feeding times and temperatures. A much easier solution is to buy some starter, or get it from someone who already has one.
A lot of us experimented with sourdough over lockdown, those long weeks stuck indoors, allowing a prime opportunity to start a new life in your airing cupboard. It can be quite daunting to manage the mercurial nature of that ancient balance of wild yeast and bacteria. Beginning the process of making your own sourdough starter alone is challenging and unpredictable; the opportunity to do so with fellow beginners and a trained professional helps allay much of the mystery and stress.