Why cant uncircumcised men have kids?

They can - there's NO connection between circumcision and fertility.

More then 80% f the worlds men are intact (not circumcised) Only 1% of Germans for example are circumcised that would mean that 1% of german men would be very busy indeed to be able to keep the country populated. Besides how did the human race come into being if they need to be circumcised to procreate.