Prolog's a surprisingly good fit for many every-day tasks where people otherwise invent DSLs or poorly-defined state machines and pattern matching algorithms.

So how come we don't use it more often? Well, the reason is actually quite simple:

Prolog's incredibly difficult to reason about once you grow past trivial facts and clauses like in the OP's article -- the examples given by him would've been introduced to you in the first lesson on Prolog in, say, University. The complexities of green/red cuts, backtracking and the procedural nature of Prolog makes it a really difficult language to truly learn -- much less one to specify complex programs in.

I've never programmed in a language where 5-6 lines of errant Prolog code could stump myself, a post grad and a professor before until I did Prolog.