UTF-16 has all of the disadvantages of UTF-8 and none of the advantages, and originally comes from the UCS-2 era where they thought, "64k characters are enough for everyone!" Unfortunately, all of Windows uses it, so we as an industry are stuck with it.
Also, Mac OS X, Java, .Net, Qt, ICU... there are a lot of support for UTF-16, for other reasons than backwards compatibility. Processing UTF-16 is easier in many situations.
Processing UTF-16 would only be easier if you have a valid byte-order mark and/or know the endianness in advance and you can guarantee that no surrogate pairs exist. Otherwise the same pitfalls exist as when processing UTF-8, plus the endianness issue and the possibility of UTF-16 programmers not knowing about surrogate pairs.
