Why should a spouse be entitled to maintaining a certain quality of life after marriage, when that QoL was a benefit of the marriage?

Referring to alimony. With that same logic, why wouldn't we force both spouses to maintain the QoL of the other one, in other ways? How about some forced sexual favors and chores so they don't lose their QoL? Super humane way of thinking...

Why should a spouse be entitled to maintaining a certain quality of life after marriage, when that QoL was a benefit of the marriage?
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