We learn from other people, from books, over the internet, many places-- over time, one tends to pick up bits of information, and after a while the total is quite impressive.
It is important to know enough to provide what your chickens need (mostly safe housing and appropriate food and water.)
Beyond that, it is mostly for fun. For any group of people that know a lot about a subject, they do seem to speak a different language, and they soak up more information very quickly when it is on their favorite subject. I've seen that with children and adults in many areas of interest. Examples include: Legos, computer gamers or programmers, Mathematicians, many kinds of scientists, English literature teachers, history buffs, fans of a particular series of books or movies or TV shows, woodworkers, knitters, quilters, gardeners, people into raising or showing any kind of animals, people making robots, tabletop gamers, etc.
It just seems to be something people do when they get very interested in a subject, and find other people who share that interest. You will tend to notice the ones who have the most to say, which means the ones at your own level just do not stand out as much.
I like to browse hatchery websites. They usually tell a little bit about each breed, often with different details on the websites of different hatcheries. I can't say whether the birds in the photos are good examples of the breeds, but they might be examples of what the hatchery actually sells

I end up knowing more about the breeds that are attractive to me, and ignoring the breeds that don't appeal to me, so my knowledge of breeds is a bit patchy.