For Groovy the simple answer is they claimed that every piece of Java code would also work in Groovy. This wasn't ever true (well, maybe before someone decided that the equals() method is confusing), but it didn't matter, because of the "80% is plenty" mindset that groovy appears to be built on.
That would justify requiring semicolons/parentheses. It doesn't justify making them optional. The real explanation is that they were mimicking another language, Ruby, that had made that mistake.
