Because in the wild these were covey birds the roosters are too aggressive to leave with just a couple hens. 1:3 is the low end of where you want to be. I run 1:6 and still have a 95% fertility rate so there really isn't much to gain by running them with less hens. If you plan to add more than 1 rooster to a cage you'll need to go from 1sq ft per bird to about 3-4 sq ft per bird and if you try to run multiple roosters with anything less than 1:5 (even that is too low really) you will have dead birds on you're hands. These roosters will only get along if raised from birth together and eventually there will com a point where they start to fight (sometimes they'll go a whole year but eventually it happens) unless you give them a ton of space and a lot of hens. There is no need to force these things to breed in an un-natural way to them, to increase fertility. Breeding cages increase fertility but if you notice no one puts up pics of their birds in breeding cages because the birds look like junk after a few months in a 9"x18" cubby with three other birds.