The two most difficult things in programming.. caching and naming
And latency.
It is just lack of knowledge or focus to understand the total execution path and remove unnecessary elements from it.
I have worked in algorithmic trading where I did research and I designed framework to respond to stock exchange messages within 5 microseconds, consistently.
5 microseconds is difficult and requires some special techniques but 100 microseconds is quite easy and requires just understanding what is execution path and removing all unnecessary operations from it.
If you look at contemporary developers and web frameworks it doesn't seem anybody puts particular care into understanding those things and only try to twiddle couple of things and see how that transfers to performance.
But then it really isn't a problem -- it is a limitation. Nothing you can do much about.
There are of course types of applications where latency is really tough topic. For one, low-latency trading is where companies are in arms race against other low-latency market players and there is always improvements form improving your product's latency.
But in a typical situation like websites and corporate services, the latencies required are so large that it is quite easy to reach them -- just don't do anything stupid.