I feel the problem here is what I imagine as this formula:
reliability * efficiency = developer skill
I.e. for a given level of reliability, you need more skilled[0] developers to be able to write efficient code. And I'm not thinking about premature optimizations here - just that the code an experienced developer will write the first time around will be efficient enough.
So in short, if you aim for certain level of reliability and employ cheap/unskilled developers, efficiency will suffer. And as long as companies don't really care about performance, developers will not gain the necessary experience to write efficient code with just-in-time optimizations.
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[0] - for "skilled" meaning probably mostly some knowledge and experience in writing fast code; it's probably not the experience you'll get when all coding you've ever done is for the web.
So in short, if you aim for certain level of reliability and employ cheap/unskilled developers, efficiency will suffer. And as long as companies don't really care about performance, developers will not gain the necessary experience to write efficient code with just-in-time optimizations.
--
[0] - for "skilled" meaning probably mostly some knowledge and experience in writing fast code; it's probably not the experience you'll get when all coding you've ever done is for the web.