Good news is that modern compilers are more than capable of emitting SIMD code even if original source is nothing but.
They're really not (I have a whole section on it in the blog post). This example in the post doesn't auto-vectorize, for example. And its a pretty big part of the overall throughput for plain text runs (ascii or unicode). Really, the point of that section is that almost nothing auto-vectorizes, backed up by LLVM docs and published research.
Instead, writing 12 lines for a 5x gain is way easier than crossing your fingers and hope someone else pays your bills.
Bigger picture, the real point is that this stuff isn't complicated. You wouldn't copy and paste 100 lines because you hope the compiler "lifts this into a for loop", you just write the for loop cause you know how and its simple.
Similarly, the common case of "process N values in parallel" is very simple. Write a dozen lines of code you're comfortable with. No need to pray the compiler people saved your bacon.