You can think of rationalize as pushing something into a shape that reason will accept. The thing itself does not change; what changes is how neat and how defensible it looks. A messy excuse, a wasteful company, an formula - each one gets pushed until it fits the frame of 'this makes sense'. Someone always decides what counts as sensible, which is why the same verb sounds like an excuse when it is aimed at a person, and like job cuts when it is aimed at a company.
From the word’s history
Wiktionary analyses the word as rational + -ize, from French rationaliser - literally to make something rational. Every modern use is that one action, aimed at a different kind of object.
字典把 rationalize 拆成 rational（講道理的）＋ -ize（使變成），來源記為法文 rationaliser，字面就是「使變得合理」。今天的幾個用法都是同一個動作，只是對象不同：一個說法、一間公司、一條算式。
Wiktionary entry for rationalize, packet etymology_text: "From French rationaliser. By surface analysis, rational + -ize."
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