Parenthesis around if/for/while condition is not necessary

[aedt]

for line in stdin.lines() {}

if condition {}

while condition {}

for init; condition; op {}


What's the rationale of keeping the requirement that the 
condition of if/for/while must be wrapped with a parenthesis 
(other than keeping parser simple)? Modern languages have already 
dropped this requirement (i.e. Rust, Nim) and I don't see any 
reason not to do so.