The West of Scotland doesn’t have a long “oo”. sound. I learned this when I first went to Germany where the short “ü” can change the meaning of a word, “bruder” for example, with a long “u” becomes plural with a short “ü”. I found I couldn’t say a long “u” without a great deal of practice.
Ritson pointed out that the spelling of words with “ui” was to signify short “u” for English readers.