That's the format for HTTP headers. They could push against the standard and accept spaces, but anything else would break your browser.
Presumably that format was fine before bigger / more complex CSP rules came along?
I find it very difficult to work with visually. Hard to see where one thing stops and another starts.
If it was up to me, I would have placed the information at the linking tags inside the HTML (and JS, and CSS), or even extended the HTTP URI format in some way. There is probably a very good reason why people decided for the header, but I'm not aware of it.