It killed the one thing C was good at - simplicity (you know exactly what happens where, note I'm not saying speed, as C++ can be quite a bit faster than C).
Now, due to language lawyering, you can't just know C and your CPU, you have to know your compiler (and every iteration of it!). And if you slip somewhere, your security checks blow up (http://blog.regehr.org/archives/970 https://bugs.chromium.org/p/nativeclient/issues/detail?id=24...) .
This mythical time never existed. You always had to know your compiler -- C simply isn't well specified enough that you can accurately predict the meaning of many constructs without reference to the implementation you're using.
It used to, if anything, be much much worse, with different compilers on different platforms behaving drastically different.
C worked in the 70s, when a naive compiler + asm would work perfectly.
Just off the top of my head, Java has the following complexities that C lacks: exceptions, garbage collection, class inheritance, generics, and a very large standard library.
What definition of simplicity are you using when you say Java is simpler than C?
I can't tell you how many projects I have been on where disabling optimization made no measurable difference in performance.
This being said, I cannot speak for game devs nor video device driver developers.
Witting them in C or VB made no difference for the guys sitting at the desk.
I've never written a business application in my life.
Teams I'm on have written some tight - but readable -code, too. Well-architected, low-latency, low-jitter.
Even more important are things that run in datacenters on thousands and thousands of machines. Even if you suppose that optimizations make only a minuscule difference on the scale of today's infrastructure 5% fewer machines can save huge amounts of electricity.
Conversely, if you maintain software that compiles on a bunch of compilers, operating systems and architectures (particularly little endian + big endian, 32 bit + 64 bit), then it's probably written in something rather like C. A lot of people do this.