It's not just "x86 is more popular, therefore better." It's that the performance of x86 was better than SPARC or Power. Regardless of the cost of the chip, performance is what is really important here. In some instances, performance per watt is more important, but either way... it's performance that's key, not market forces driving cost savings.
I haven't had much experience with SPARC, but I've done some work on Power systems (long ago). Back then (10-ish years ago), Power chips were more powerful than their x86 contemporaries. But at some point, that relationship switched.
However, I wonder how much of this is the chip, and how much is the tooling. Its been awhile since I've needed to think about C/C++ compiling, but from what I remember, the Intel compiler produced (slightly) faster binaries than gcc. Now this is where popularity could prove to be decisive... if the compiler that the OP uses works for x86, SPARC, and Power, how much do you suspect each of those architectures has been optimized? Even if the non-x86 chip itself is capable of running faster than x86, if the toolchain isn't similarly optimized, they could end up having worse performance.
I haven't had much experience with SPARC, but I've done some work on Power systems (long ago). Back then (10-ish years ago), Power chips were more powerful than their x86 contemporaries. But at some point, that relationship switched.
However, I wonder how much of this is the chip, and how much is the tooling. Its been awhile since I've needed to think about C/C++ compiling, but from what I remember, the Intel compiler produced (slightly) faster binaries than gcc. Now this is where popularity could prove to be decisive... if the compiler that the OP uses works for x86, SPARC, and Power, how much do you suspect each of those architectures has been optimized? Even if the non-x86 chip itself is capable of running faster than x86, if the toolchain isn't similarly optimized, they could end up having worse performance.