It's self-evident from interacting with a wide range of developers, but I suppose I can prove it no more than I can prove to you the sky is blue. I'm not saying there aren't cases like yours of "I could optimize it, but I'm not being paid to". But there are also many, many cases of "Are you crazy? I would have to spend my entire life learning about CPUs, compilers, assembly, and programming languages! Get real, nobody can do that unless they're a 1% genius" for things that they could absolutely learn to do if they just tried instead of living in fear of it.