Compiler writers have to use program transformation to do well on benchmarks. Developers who don't prioritize benchmarks probably don't use C, and if they do they really shouldn't, because sacrificing correctness for speed is the only thing C is good for these days.
Speed isn't the only reason to use C. I often use C not because it's fast, but because C is by far the simplest mainstream programming language. All these UB warts notwithstanding, no language's interface comes as close as C's to a basic, no-frills register machine.
Yeah, we must have different definitions of simplicity, as I expected.
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?
