[0] Modulo that Python et al almost certainly have order(s) of magnitude more external libraries etc.

Prolog has many implementations and you don't have the same wealth of libraries, but yes, it's Turing complete and not of the "Turing tarpit" variety, you could reasonably write entire applications in SWI-Prolog.

I don't think I ever learned how it can be useful other than feeding the mind.

    let prologBlob = new ProLog()
    prologBlob.add( "a => b" ).add( "b => c" )
    prologBlob.query( "a == c?" ) == True

There's so much stuff regarding constraints, access control, relationship queries that could be expressed "simply" in prolog and being able to extract out those interior buts for further use in your more traditional programming language would be really helpful! (...at least in my imagination ;-)