Sure, romantic and erotic love have always been part of human literature and history, but for most of history marriage did not always means love. Love was like an extra, a good-to-have, while marriage was vital to have children and a stable home to raise them, and also to grow old with some support. It was a retirement, a project to have children, and a project to accrue assets. Sex was a requirement, but love was not.

In a sense, marriage was more like a job. You don't have to necessarily love your job or your boss... you may love aspects of it, you may like your job sometimes or partially, and ideally you have a job you love, but it is not a requirement to have a job and get an income. So was marriage seen. Sometimes men and women did not like each other in marriage, and yet they were able to raise healthy big families, care for each other, accrue resources, etc. Today, that kind of marriage is kind of unconceivable.

These days, marriage does not only have to be all of that (the basic requirements to have kids and resources), but also it requires your partner to be your best friend (a relatively new requirement), to make always you happy, to be X way physically, have Y education, etc. The requirements went to the roof to the point that, even lacking on of those requirements, can be enough for people to rather stay alone or keep looking forever. Conditions keep adding by the decades, creating a strawman platonic idea of love and marriage that is not very sustainable long run (hence, the divorces).

The irony is that we don't need marriage to survive anymore, and yet the requirements were to the roof! In the same token, men don't have to be strong and tall to survive anymore, and women don't have to be fertile and young for couples that don't want kids anyway, and still those requiremens are very high today. Marriage now is a luxury, a way to cause envy on others. Imagine getting 70k in debt just a wedding, and yet people see that as normal and even expected if you "love" your partner or some shit.

The sugar daddy relationships are kind of sexual arrangements, but they are very to how traditional marriages used to be. Men gave resources in exchange for fertility and sex. The main difference seems to be the fact that they are not expected to stay together for life. This is a disadvantage for the wife who probably loses her youth and fertility in this, but also for the man who cannot expect to build any kind of family or stable home, yet if she is looking for money and he is looking for sex, it is the most ideal arrangement.

TLDR: Sugar daddy relationships are closer to how historically marriages were, with some minimal essential requirements rather than endless unrealistic requirements, but SD relationships are centered around sex and money. SD relationships have the sexuality and money interest of modern relationships with the minimalism of true traditional marriage (not the boomer divorce shit marriage).