No games? What about 4, Prologue, PSP and 5?
That covers 2004-2011. I would be willing to bet a lot of the marketing for years 2007-2011 was mainly to keep a bubbling interest in 5 if anything because Sony really needed it as a major title for the PS3.
Now that GT6 is not likely to be around for a while, we see that GT/Playstation sponsorship has been reduced.
Of course, it could just be that SCEE/Sony France have decided to step back with their budget as they have always had a small presence if only as a sponsor to one or two cars (its worth noting its usually been french teams that they have sponsored e.g. Pescarolo, Oreca, Peugeot, Labre..even Prost in F1).
Or maybe they just feel GT Academy is doing a much better job (which it is) and so any additional sponsorship or marketing is a waste of time and effort when everyone is already talking about it.