The price point of the i3 ~100 dollars, and the fact that most applications will not be CPU bound by an i3 are the driving factors. The clock speed is one thing, but the instruction sets really provide everything that's needed that would otherwise peg your cpu (notably quick sync, but also aesni, avx2.) It's a testament to bad software (minus games) if the thing you're running can't be handled by an i3 with ease.