SEO is important because it allows you to reach the audience you want, and give them what they want.
This is a difficult thing to explain in words, but it’s really easy to see with an example. Let’s say you have a website about yoga. You could go out and find people who practice yoga, and then put up some signs at their favorite yoga spots that say “Yoga Class Tonight!” That might work, but it’s not going to be very effective if nobody knows that there’s a yoga class tonight.
That’s where SEO comes in—it helps people find your content when they need it. If they’re looking for something specific, you can help them find it!