Earlier this month AMD cited low market demand as the reason why Skybridge had been cancelled but now there are rumors that suggest it would never have been possible to launch a cost-effective version of Skybridge on time. GlobalFoundries decided to kill its 20nm process and that may have left AMD without a launch platform.
Roadmaps from GlobalFoundries show that after the foundry signed its deal with Samsung, it has indeed cancelled its 20nm LPM node, presumably to focus its resources on the development of 14nm to serve as Samsung's second source. Perhaps GlobalFoundries was willing to build out 20nm capacity for AMD, provided the chip designer fronted the cost of doing so, but AMD has made it very clear in its recent company presentations that it isn't interested in investing in custom process technology lines.
If AMD didn’t want to pay GlobalFoundries for an exclusive process node, it could theoretically have taken the chip design to TSMC. Sunnyvale did this once before, when GF couldn’t build its Krishna and Wichita APUs (these parts became Kabini and Temash). The decision to redesign the hardware, however, pushed introduction dates back a full year. Taking Skybridge to TSMC means ramping multiple designs on the short-lived 20nm node — designs that would be pushed back into competing with Zen and possibly K12 depending on bring-up timing.
GlobalFoundries node cancellation could also explain why AMD paid no apparent penalty for failing to buy as many wafers as originally forecast. Normally, failing to purchase its expected quota of silicon wafers from GlobalFoundries would incur a penalty, but AMD didn’t pay one in 2014.