Picture a body as something with unwanted stuff built up inside it, and a stretch of days set aside to get that stuff out. Nothing is added during those days; things are only taken away and waited out. That stretch of time is what detox names, and every use of the word keeps that shape: a period, a clearing out, and someone waiting for it to finish. The word itself is a long medical term, detoxification, cut short — so even its shape is something trimmed down to what is left.
From the word’s history
Detox is a clipping of detoxification, the word for removing toxins; the short form keeps the whole picture and just drops the long ending.
detox 是 detoxification（去除毒素）剪短來的形式。字根 toxin 就是毒素。剪短之後畫面完全沒變，只是把長長的字尾丟掉了。
Wiktionary etymology supplied in this packet (kaikki:3f6f69a190036ae4): 'Clipping of detoxification.'
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