XQuery uses one language that can do both. I think it is a given that some people will never see a reason for XQuery, since XSLT exists. There is a sizable community of people who do see a reason for XQuery. I remember when people were really confused about why XSLT was needed. Object orientation was invented in 1967, but object orientation was not mainstream until the late 1980s.
New technologies take time to understand and appreciate.
Of course, hogwash takes time to recognize and discard. Eric van der Vlist was sympathetic to XML Query. In his view if the new language is better fitted for some uses, then everyone may benefit . If it happens that the new language is a better fit than XSLT to do some of the tasks I have to do it will save my time. Some competition between may be a good motivation and I would rather regret that XSLT has been lacking credible competitors and alternatives for such a long time.