It's not about the fact that you couldn't paint coloured squares on canvas Rothko-style. Quite possibly you could. It's that he did it first. There are tons of artists in certain Chinese villages who have perfected the art of pointilism possibly almost as good as Seurat (certainly indistinguishable for an amateur's eye), yet their paintings sell for a couple dollars, not a couple million.
You could also easily extrapolate your argument about scribbling on the canvas to the realm of software development and argue that creating e.g. Facebook or Amazon or Wikipedia is really nothing special. A few lines of code will get you a usable MVP. I'm sure you could have done it (I'm saying this completely unironically). However you didn't. Someone else did it first. There may be dozens or hundreds of copycats but the original idea and/or the successful marketing of said idea is all that counts. The rest is noise (sometimes rightfully, sometimes not).