As I am thinking this through, there is really little difference between mono and poly except mono are poly in time (one partner at a time) where poly can be mono in space (dedicated to multiple partners in different places since it is physically impossible to be two places at once, or for two people to be in the same space as once).
Then there is the quantum aspect where you share time and space the closer the members of a poly family are at any one time.
Okay, I'm done being flippant.
Having now been married for nearly 9 years, even had I identified as poly (or my wife) I don't think either of us would have had the time nor energy to have been so, given how much work it is to create one single relationship, ours, to the quality we wanted to.
There's phrase in the tech industry I think applies; More wood behind fewer arrows.
No matter how many poly relationships you want, you are always going to be limited by time and energy. On top of that you have the long, intricate, delicate, and time consuming process of forging the relationship. If you are lucky you 'work out' perfectly with very little effort, and so both of the time and energy for more relationships.
Statistics work against you, however, because each additional relationship is unlikely to be as perfect. I distinctly recall 'loving' multiple girls as a teen, and later a young adult, but didn't think I could manage multiple relationships even a year ago, especially a year ago, after having the experience of being married to my wife for so long.