More precisely, alpha males are the ones which lots of women want to have sex with. Mick Jagger (in his prime), for example, was not "bigger and stronger" than other males, but he was very definitely an alpha.
Beta males are the ones that women "settle" for, when it becomes evident that none of the alpha males who she slept with displayed any interest in actually marrying her. Betas are good providers, but unexciting.
With Alpha males, it is just easier to go through a succession of bed-warmers than to go through the trouble and struggle of maintaining a relationship with any particular woman. One of my college friends comes to mind: tall, handsome, intelligent -- all the girls wanted him. I was catching up with him a year ago. He never married.
Even black people go, "He got some big-ass lips." - Eddie Murphy
I tend to agree with you. A beta male, who has a prodigious amount of talent in an area, that can lead to a lot of wealth creation will become more desirable. Many of the notable scientists and authors, like Einstein and Huxley, were notorious womanizers.
I also agree with you that many of the attractive males tend towards unstable relationships because they’ve don’t have to learn how to please their partner because there is always another one around the corner.