I don’t think anyone understands ALL of them.

As you become familiar with a certain style, you notice differences between them. The deeper you dive and the more you listen to, the finer details you can recognize.

I could probably name at least 25 different genres of rock, and explain how they are different, but styles I’m not familiar with, I can usually only recognize the broadest category. Bluegrass all sounds like bluegrass to me, but an expert could identify 25 different subgenres of it.