Not sure point One is fully correct. I think they often realize things is going to be shitty for everyone, but they think it will be less shitty for them if it gets more shitty for others. They know they will be an exploited working class (even if it is not phrased that way for them) as long as there is a part of the working class (immigrant workers, women workers, …) that is beneath them it makes them feel more ‘on top’.
That only covers one angle, if people do it for religious reasons, not if they don’t do it because of religion. I’m not getting married, and the religious connotations of even a secular wedding is a significant chunk of why.
If you trace back the cosmological evolution of our universe you’d get a “singularity”, that is not the same thing as being a single particle. Even the physical existence of a singular point at the beginning is not accurate. A singularity in physics is a mathematical artefact signaling the breakdown of the descriptive power of the theory you are using. The common example is the singular behaviour of the electric field around a charged particle in classical electrodynamics, the singularity is a signal that you’d need to switch to quantum electrodynamics to describe the physics close to a charged particle. Similarly with cosmology: close to the beginning we have a singularity that signals the breakdown of the descriptive power of our theories, and we need to switch. What we would switch to we call a " quantum gravity theory", but we are not yet sure what that theory is.