I honestly think for the sorts of websites you make in SquareSpace, they shouldn't be. There's no reason that to develop a static website (even with some dynamic elements like a shopping cart) that you should need e.g. a build process to target modern browsers (i.e. consumers in Western economies).

But this is probably me being idealistic. It's why I like things like hyperscript... it feels like we might be _just_ on the cusp of what I'm saying being true.