XML is well regarded in the enterprise and languages like JAVA, C#, and VB.NET handle is spectacularly as an exchange format. I think it's bad reputation comes from anyone not using an enterprise language because the support just isn't there. I recall working with a partner who we were doing an identity federation with. Our system was using WS-Trust which is a SOAP/XML protocol. It wasn't ideal but everyone seemed to…
With a language like Ruby, PHP, etc that isn't strongly typed it's not nearly as big of a deal. Developers in those languages are used to assuming everything is a string and converting it to something useful without the need to premap every datatype.
That's probably the main reason that XML was so much more popular with the languages you mention compared to the parts of the ecosystem that didn't benefit from it's constructs much (if at all).