How did ‘concern’ semantically shift to mean ‘commercial enterprise '?

No, it's not a "concern" in the sense of "worries". It's a concern in the sense of "commercial enterprise, entity".

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PS: From the sense of busyness came the business meaning of “concern” I suppose.

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1. How are these 2 senses of concern related? What semantic notions underlie the popular sense of 'worries', with this esoteric sense of 'commercial enterprise'? I need much more detail than these snippety sentences above.

2. Please trace all semantic shifts from Latin concernō (“I mix, sift, or mingle together, as in a sieve”) to this sense of English ‘concern’? How, and why, did concernō shift to ‘concern’ meaning "an establishment for the transaction of business"?

I never heard of this 'obscure meaning where it means "business"'!

FYI a "concern" is quite old english for an establishment or business of some kind.

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3. But why use "concern" when "business”, "corporation", or "enterprise" are more intuitive and understandable?

First of all, I beg to differ that concern and the others are exact synonyms. They are somewhat synonymous but there are shades of difference in their meanings. Second, intuitive and understandable are subjective perceptions that others may not share. And third, how could anybody trace all the semantic shifts that have occurred gradually over a span of 2,000 years from a Latin root word to its present day descendant in English usage?

probus said:

third, how could anybody trace all the semantic shifts that have occurred gradually over a span of 2,000 years from a Latin root word to its present day descendant in English usage?

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Others did so here for adjacent, elude, gerund, -rogative. I am seeking such answer.

I'm not at all sure what you're looking for. Do you not understand how that word is used? Or do you approve of some usages and disapprove of others?