Re: Inefficient ???
Answer : because its NOT "exceedingly inefficient" by any reasonable measure.
No, the real answer is much simpler than that: Intel's chequebook. Look at how many companies adopt the latest generations of semiconductor fab - there used to be a dozen or more at the cutting edge, now it is essentially Intel and everyone else is at least a generation behind. No-one else can afford to roll out a number of $10 billion dollar plants. All that manufacturing tech is going on one thing: redressing the huge disadvantage that the x86 architecture brings.
This is old news: consider what is now almost 30 years ago, Stanford MIPS and the Intel 386 were released in the same year. On the one hand you had the dominant commercial player with the deepest pockets, on the other you had a small university research team. Guess which of them produced the processor ten times faster than the other? If x86 is so efficient how is that even possible?
Of course things have moved on since then, Intel have gone down the route of ever longer pipelines, ever smarter branch prediction and ever larger caches. A lot of that silicon area isn't being used in a particularly desirable way, it's simply engineering their way out of a corner. If you have a pipeline 20-odd stages long that isn't good, it's insanity - as the pipeline gets longer the number of difficult corner cases that need to be addressed (branch prediction misses, values of operands that are unknown etc) increases exponentially. Fixing them all requires yet more silicon and yet more engineering, resources that given a more efficient architecture could be used to greater effect elsewhere.
Again, that isn't news. Cast your mind back now only ten years. The engineers at Sun looked at how pipelines, branch prediction and caches were steadily becoming more and more complex and they asked themselves if that was really a sensible approach. They decided not and went for a much simpler design with a large number of threads and a large number of cores. At the time of its release the result, Niagara, was the world's fastest microprocessor bar none. Again, from a design team with a small fraction of Intel's resources. Why can't Intel tell a similar story?
Intel have some of the best VLSI engineers out there. Year after year they manage to make processors that perform reasonably well essentially by throwing money at the problem, both the design budget and investment in first-rate manufacturing facilities. That does not make the design itself efficient: give them a clean slate and the same level of resources and just imagine what they could come up with.
Biting the hand that feeds IT
