[tgv]

As other people have said, boxes and lines is another way of representing order, or sequential steps. You can also do that in text.

But you're right that there are other ways. Scratch is an example. But most programming languages are relatively close to math notation, and that appears to be convenient for us.

If you want to see a programming language that works entirely differently, yet still has a graphical representation alternative in boxes and lines, look at CSound. It's an (old) language for generating sound, but its representation is different.