Re: Why do some people remarry after decades of Marriage?
Why remarry? I suggest that you read Dr. Sue Johnson's book Hold Me Tight. It explains that people are social animals and the all primates have a huge need for companionship. We also have huge need to people to people physical contact, i.e. touch. In this age of STD's/STI's, etc. marriage is one way of having intimacy and touch that is considered by most to be socially acceptable and understandable. If you marry a man then your children will not be as likely to objecting to you living with him or having sex with him.
I can understand your approach of how could I find anyone that would replace my spouse. However, you might also want to read the book Still Sexy after All these Years. It is a collection of short stories, based on interviews of women over the age of 50 who have for one reason or another (death, medical condition, divorce, etc.) no longer have a spouse or significant other in their life. It is all about how they find ways of including either sexuality or sensuality within their lives. Please check it out of the library and read it. It was recommended by the sex therapist that helped save our marriage as something to think about if my wife refused to work on saving our marriage.
A final reason in this day and age is money. Some pensions only pay the former worker and not a surviving spouse. That could be a pretty harsh reality for some without a lot of financial means. It also is true that two can live together less expensively than two in separate households.