It's something that comes from Haskell. The `where` keyword always starts a new layout/indentation context. It's not strictly necessary and there are ways around it, so it's just a point of consistency.
Yes, I'm not saying there aren't usages for them in general, but PureScript currently occupies a niche that doesn't get down to the level of binary file formats. This change is more about "only supporting what we need to right now", rather than "we don't like binary literals". As noted elsewhere, it's not difficult to add support for them when we need to.