Your post is fascinating, Shipwrecked. Some of what you say is very much in line with my own experiences with poly. Not sure why anybody would call you shallow? Anyway.
1. The pool of potential partners drastically shrinks with time.
Yep - I have a bunch of friends who were poly when they were in their 20s (and 30s for at least one in the group). None of them are now. For a variety of reasons. At least one just prefers monogamy. At least one has a partner who doesn't want to be in a poly relationship. At least one couple have decided that it's just too much work to make it work.
So yes I'd expect that dedicated poly folks will have a smaller pool and I'd guess that'll start to happen as you get into your 30s and 40s which is when most people seem to settle down and start families.
4. A history of polyamory diminishes your ability to find partners outside the poly community.
I would guess this to be very true. My SO spent much of his 20s and 30s in poly relationships and when I started to see him people used to take me aside and warn me that he wasn't to be trusted. That he would cheat - he has never cheated on a partner.
Others would tell me that all of his past girlfriends have cheated on him. Again - not quite true. He was just in poly relationships.
My SO and I are monogamous and have no plans to change that right now. I'm friends with some of his old lovers and I have had people be appalled when they've found out.
My experience is that there is a deep seated mistrust of poly relationships around in general and I'd guess that people who have been poly may find it harder to gain the trust of a partner who has always been mono.
Paradoxically, the richer one's environment is the more sense monogamy seems to make. Particularly as you age.
Yes - I very much agree. I have a rich, full life. I have made space in it for one romantic partner and I very much enjoy having him in my life. But - I don't want more of that. I have lots going on that I don't want to give up. Nor do I want to be knackered all the time from dealing the emotions of juggling multiple relationships or having a partner who is doing so.
Having said that, I was very happily single for about 7 years and I don't necessarily feel the need for any romantic partner in my life. I like it but I have lots of wonderful friends, family and interests in my life that I can happily live without a romantic partner indefinitely.
Why I Took the Time to Write This
I have a theory that it might well get easier again with age. It seems to me that people in their 30s and 40s are busy building homes, careers and families. I would guess that maybe in people's 50s and 60s and older it might be easier to be poly? Or at least easier to find relationships.
I don't think you should write your chances off whatever age you are.
And - even if you are single from now on I also don't see that as necessarily a bad thing. All of us living in the West get to live lives of utter luxury - we have so much going for us and so many options open to us. Be a shame to waste opportunities because of pining for love.