Besides there're many posts claiming, it first appeared as representing a hamburger's meat inside 2 of it's breads as this link states, I also believe (or naturally understand) it gives user the feeling there's a lot more to discover when clicked, since
"..." punctuation has same meaning abstractly in grammar that
gives readers an understanding of sentence is continuing.
Besides I couldn't ran into any standart about this on any WCAG document, using other than 3 lines/dots not necessarily gives the same experience like using a single or twice line/dot. And using more than 3 lines not desired I suppose since it's enough to emphasizing it with less.