I don't understand alimony culture

alimony is about equitable distribution of gains earned during a long-term marriage. it's a literal math equation. the amount and term are determined through a literal mathematical formula, so that one does not end up at a disadvantage. say you're married for 20 years as a mostly stay-at-home parent, with several children spanning in age, so you don't spend as much time in the taxable workforce while your spouse advanced in education, work experience and credits towards social security the entire time and then decides to divorce you. will you be needing your fair share, or can you afford to just be devalued and expected to catch up to your former status of living with none of the support your spouse received during the marriage?