Well that comes back to what I always come back to on this list. XML is to complicated, and that complication necessarily manifests itself in fully compliant tools.  Developers have come to hate XML and just want to crowbar, chisel and scrape it as quickly as possible into a structure that they can actually understand, using a tool that seems to hate XML as much as they do.

I wanted to know whether there was anything more to it than this. The same set of people that will decry parentheses in Scheme or angled bracketed markup will happily type in hieroglyphics at a mongodb shell prompt without a murmur of protest. So it's not based on rationality then.