But 11gR2's continued longevity should not be a surprise.
For a start, it is a really good product. It is fully-featured and extremely robust. It offers pretty much everything an organization might want from a database. Basically it's the Windows XP of RDBMS.
The marketing of 12c has compounded this. It has focused on the "big ticket" features of 12c: Cloud, Multi-tenancy and In-Memory Database. Which is fair enough, except that these are all chargeable extras. So to get any actual benefits from upgrading to 12c requires laying out additional license fees, which is not a popular message these days.
And then there's Big Data. The hype has swept up lots of organizations who are now convinced they should be replacing their databases with Hadoop. They have heard the siren singing of free software and vendor-independence. In reality, most enterprises' core business rests on structured data for which they need an RDBMS, and their use cases for Big Data are marginal. But right now, it seems easier to make a business case for the shiny new toys than spending more on the existing estate.
So how can Oracle shift organizations onto 12c? They need to offer compelling positive reasons, not just the fear of loss of Support. My suggestion would be to make a couple of the Options part of the core product. For instance, freeing Partitioning and In-Memory Database would make Oracle 12c database a much more interesting proposition for many organizations.