K’shmo, the fact that there are parentless children, does not mitigate the pain of people who desperately want to have children from their own bodies. A woman, in paerticular goes through a terrible nisayon when she has trouble in conceiving. You have no idea what it msut be like for her to go through month after month of Mikvah attendance, with the knowledge that she is infertile.
Yes, you are right, there are many kids who could benefit from loving homes, and I urge people who know they definitely CANNOT have children with their DNA (or those who have borne children but want to adopt), to offer loving homes to those kids. The mitzvah of pru urvu is still incumbent on us, and we should help people to be mekayeim it when we can.