Then how did ARM succeed?
Because they're from an earlier era. And for what it's worth, they're the exception, not the norm. Silicon Valley is rather akin to the restaurant industry... for every business that succeeds, ten fail.
They also exploited a big gaping hole in computing... that low power hole is filled, and we're seeing the industry consolidation that happened in the 90s for x86, now for the smartphone market.
The problem that AMD's having right now is with money. It's actually very clear. Ever heard of the project management triangle? Idontcare's talked about it a few times.
You can either keep costs down, delay your time to market, or cut back on the quality of your product. You can pick two at most. AMD doesn't have a choice but to cut back on costs, and they've chosen to keep their time to market down. However, their quality has suffered. We've got 2, arguably 3, and potentially even four products (if Seronx is correct about Kaveri having disabled GPU and CPU logic) in recent history that are perfect examples of this.
Bulldozer needed another year in the oven before Vishera markedly improved over it. Trinity was a wash compared to Llano in terms of CPU performance (the arguable one I mentioned before), whereas Richland provided a fairly significant performance boost without even changing the silicon. Jaguar products were blown away by Puma. If Kaveri does in fact have Excavator cores and disabled GPU logic like Seronx has suggested, that'd be a fourth product to follow this trend.
AMD simply needs cash. You can't argue other otherwise, unless you're misinformed or intentionally ignoring AMD's precarious situation.
At this rate, if AMD makes it long enough to deliver K12, it's probably going to be another disappointing launch, followed by a later revision to significantly improve on it. Perhaps the console bucks they made last year could fuel a decent product, but they need to keep that cash flowing. AMD's got some wonderful talent, even after loosing a fair bit of it, but you need money to get the kind of manpower to keep up with your competitors.