Add the years since Todd Howard arrived on the scene we may be able to see the reason for TESVI's delay. Todd was 17 some time just after the Arena.
That was back then he was a lightning rod and charged the ground around everyone so MORROWIND, OBLIVION, and SKYRIM practically EXPLODED onto the PC video game scene.
Now we have a tired older Todd whose burst of caffeine lightning bolts are just occasional spirts on the scene on camera. Then he starts flagging just after he starts feeling the drain and gets off the stage before he starts staggering. His Lightning charged habit has given him a tolerance so he doesn't get a big charge from Red Bull or Rock Star, not even Starbucks super duper Espresso', that children miss pronounced calling it Xpresso, for a long time.
Pat Sajak's Italian wife and Vanna White's Italian husband may have had something to do with Pat telling the world on the show The Wheel of Fortune that it's not Xpresso' it's Spresso'.
If Todd got to know someone with a coffee bean roaster and learned to roast his own coffee beans he'd be back in the saddle in a short while. He's probably reluctant to do so much caffeine anymore as he's likely more than a furry, lover of Khajiit, he may have a real home life now.