I see three drivers for this true observation:
I'm a very observing information technologist I would say and RDF has been on my radar for I would say 6 years. My sentiment towards RDF until about one year was:
- Very popular in academia
- Complex if you want to do advanced stuff
- Clearly the basis for the Web 3.0 but needs time
Considering the the major architectural paradigm in which at least larger commercial organizations lived and still live: SOA, ESBs.
They were just happy to have their interlinked silos and not isolated silos. Their biggest challenge was and still is to integrate systems. Many of these systems is COTS and they have no control and nor interest in the exact details of the employed data models, they just want to import and export data from those systems.
Also consider what major vendors in the IT sector brought to the table:
I know of RDF support in Oracle and DB2. I even played around with it on DB2 a bit and my opinion about their efforts is rather crushing: Not really usable. I thinkk that they merely added support for some SemWeb stuff as marketing alibi - just to have it and not being reckoned to have overslept a trend.
I think all these 3 lead to the situation you described.
I'm 100% sure this will change and soon be visible in Gartner's Hyper Cycle as big, open and linked data trends mandate a interoperable data model/ serialization format.