[pavlov]

XML is certainly declarative.

As far as CSS goes — ask any front-end web developer if they would like all programming to be more like CSS...? It is a collection of thousands of properties, often overlapping or contradictory, some with their own sublanguages for further specification, and many features are defined as hidden side effects of one property when nested inside another. A total mess.

You can only declare what you want if the language lets you say it. (Think of Wittgenstein’s famous maxim.) SQL was a great design informed by decades of research. Most software designs are not like that, unfortunately.