One way to hold this word: you put something in, you wait, and at the end nothing is left over. That leftover is what profit means, and un- ... -able says there is none to be had. When what you put in is money, the leftover is money, and the word is the plain business one: a shop, a route, an app that does not pay. When what you put in is time, effort or talk, the leftover is any kind of gain, and the word says the hour is gone and nobody is further forward. Same picture, different thing poured in.
From the word’s history
The word is un- plus profitable, which is built on profit; profit itself once meant gain of any kind, not only money, which is why the wider sense does not feel like a stretch.
這個字是 un- 加上 profitable，而 profitable 建在 profit 上面。profit 本來泛指「得到的好處」，不只是錢。所以「沒有收穫」那個用法並不是硬掰出來的，而是保留了這個字比較舊的範圍。
Wiktionary entry for unprofitable (kaikki extract, source_ref kaikki:3f6f69a190036ae4:1239711437): "From un- + profitable."
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