Why no combining‐character form for U+00F8?

Having just been to Norway, and wanting to email my friends all about
it, I came across a curiosity: neither of the combining characters
U+0337, U+0338 seem to work in usually‐reliable Emacs, and indeed
U+00F8 LATIN SMALL LETTER O WITH STROKE doesn’t seem to have a
decomposed form, according to UnicodeData.txt. I’m sure this can’t be an
oversight?

-- 
Ian ◎