This has in fact been debated back and forth on the es-discuss mailing list and in TC39, especially given experiences with strict mode. The decision was generally made to not have more modes and to just have a single JS language.
You don't have to agree with that decision obviously, but this isn't something that happened willy-nilly.
You don't have to agree with that decision obviously, but this isn't something that happened willy-nilly.