The reasons are complicated but, many people prefer unicode normalization so that different forms of what appear to be the same word are considered the same word. People argue whether or not this is important but it can certainly be argued that it would be frustrating to get an error like
let café = 1;
café += 1; // error, unknown identifier 'café'
The error happens in non-normalizing languages because those to idenifiers are not the same unicode.But, choosing a normalization affects emoji as well. Worse, when new ones are added the normalization rules can change.