These aren't the same thing. Brainfuck is "simple" in the same sense - no hidden behaviors or complex syntax - but it's virtually impossible to tell at a glance what a Brainfuck program does, or say with certainty how it will react to different inputs. Complexity has to live somewhere, and the more restrictive the language, the more complexity is moved to the program structure. Conversely, every special-purpose construct in a language is a place where you don't have to rely on reasoning about an unboundedly complex Turing-complete system, and can instead go and check the documentation for what it does.
These aren't the same thing. Brainfuck is "simple" in the same sense - no hidden behaviors or complex syntax - but it's virtually impossible to tell at a glance what a Brainfuck program does, or say with certainty how it will react to different inputs. Complexity has to live somewhere, and the more restrictive the language, the more complexity is moved to the program structure. Conversely, every special-purpose construct in a language is a place where you don't have to rely on reasoning about an unboundedly complex Turing-complete system, and can instead go and check the documentation for what it does.