Given the cost of marriage and divorce, it makes far more sense to live alone. I've been married twice and I learn this the hard way - twice too many times!
Additionally, the simple fact that is that woman are responsible for 80% of budget decisions which tend NOT be be things men would buy, so if you are a single man, NOT pairing off sudden save/raises your income by 5x if you don't marry.
https://ifstudies.org/blog/want-to-avoid-divorce-wait-to-get...
Of course you are correct that lowered social stigma associated with divorce is also important. This topic must be difficult to study over very long periods of time, because so many things are going on (changing age of first marriage, reduced social stigma associated with divorce, women's liberation, changing religiousity, etc. etc.).
For some problems, this is indeed the absolutely correct decision - but it simply wasn't culturally acceptable in the past.
Musing out loud… I wonder how much TV has to do with the decline of shared households. Perhaps in the 1920s I would have happily lived in a boarding house with other unmarried workers. These days I’d have to really love someone to make myself subject to their choice of television programming, which is generally inescapable in a shared apartment.
I totally get the desire to live alone, but I never have because having roommates/cohabitation always seemed like such an obvious economic decision compared to other ways to reduce living expenses.
The Onion put out a video[1] in 2009 about an economic recovery plan that amounted to boyfriends finally agreeing to move in together with their girlfriends. I've spent a lot of time researching the housing market and macroeconomic reasons for its current distortion from historical norms. That video often pops into my mind when I do. The overall housing stock in the US has more than kept pace with the growth in population, but the reduction of household size and related growth in housing space per person has created a huge amount of incremental demand.
I don't think those are purely bad trends. My parents' generation paired off young and quickly, and the long term effects are easy enough to pick out in divorce statistics. But I do have to wonder how much of the economic woes 20-40 year olds face right now might be alleviated if the pendulum swung back a little in that direction.
[1] https://www.youtube.com/watch?v=7ADncN9HIa4