kiya

Assume that every factor drops a person's chances by one in ten, because that way the math is easy.

This means that finding a partner under most circumstances (monogamous or poly) is a one-in-a-thousand chance (or, if you consider 'being poly' a factor, one in ten thousand):

someone you find attractive
who finds you attractive
who is poly/poly-friendly
with whom a relationship could be worked out

(Note that I'm rolling all of the actual human compatibility shit into 'with whom a relationship can be worked out'. So all the possibilities of incompatible politics, odious personal habits, simply unable to work the logistics over the circumstances, wanting children or not, discovering after five years that there is a painfully unresolvable incompatibility, and so on, is being lumped into a single factor.)

I don't know about anyone else, but 'one in a thousand' or 'one in ten thousand' strikes me as about right for what fraction of people I encounter might be potential partners, and even with those numbers if I plug in the population of the city in my profile I get 70 or at least 7 potential partners without considering travel.

Package-deal relationships, on the other hand, require:

someone who finds you attractive
who you find attractive
who finds your partner attractive
who your partner finds attractive
who is poly
who is willing to touch a package-deal relationship setup with a ten foot pole
with whom a relationship could be worked out

Which is one in 10,000,000, and unlikely to live in my town or yours, though according to Wikipedia's current population notes, there are probably 31 in the US.

If one adds the standard UH criteria of "for an exclusive relationship", you've got added to that: