Those technologies don’t get traction I think because for most common practice uses of XML they aren’t that useful.   Most useful related office data is stored relationally.

As Tim Bray observes, XML thrives as bits on the wires.  As a representation most programmers can schlep in and out of RAM as documents, it’s ok.  Most common uses can use microformats for the longer lived semantically loaded bits because microformats track the average information density of tables.  Wise URI management does the rest.   If you need a doc of links, you usually have a table of contents or the reverse index which is fine because those are where some of the ideas in XPointer and XLInk originate as well as glosses/annotations.

Very complex abstractions of semantically loaded data can be fascinating to think about, but what practical desktop uses are made of them?  I’m not saying they don’t exist, but where they exist in the information ecosystem, what other systems are their dependent neighbors?

Humans read the stuff.   Documents work.   As a result, the most frequent user of the system doesn’t use XPointer or XLink.  They don’t care.   No care: no market.