Because they do not know better.
The only valid criticism to utf-8 is that encodings for common Asian languages are oversized from other encodings.
UTF-8 is superior because
- It is ASCII compatible. Most known and tried string operations do not need adaptation.
- It is Unicode. Anything that isn't Unicode shouldn't even be considered in this day and age. If you have important data in encoding X, spend two minutes on Google and write a conversion function. Even if you have to interface with sourceless legacy app Z, you can run your communications through a pipe so that your logic stays in the 21st century.
- UTF-16 isn't fixed length either and assuming it is like many do, will only cause terrible bugs.
- Additionally Unicode is very complex and it is almost certain than any fixed-size algorithm adapted from ASCII will yield bad results even in UTF-32.
Say you have this UTF-16 string.
[0][1][2][F|3] [4] [5]
And you want to insert a character with code 8 between [3] and [4]
you would do insert(5,8)
If you don't check for characters outside BMP(serially as in UTF-8 as you cannot know how many double sized characters you have) you get:
[0][1][2][F|8][3][4][5]
Two new garbage characters. So much for your fixed size encoding.
You can of course disallow such characters altogether, but then when your code interfaces with the real world, you might find your program saves the profile for this user who lives in rm -Rf / in .profile instead of [Classical Chinese Proverb].profile.
Or just an angry user that cannot write his thesis on Classical Chinese Proverbs with your software.
