Doesn't adoption make much more sense for the majority of people?
I think people simplify adoption as the "answer". Adoption isn't just like picking a child like a toy off a shelf. It takes a very special person/family to adopt a child because they may have special socio-emotional needs. Children who are given up or orphaned often struggle with self-identity and/or feelings of abandonment. Some parents may not be prepared to deal with these challenges even if they have a world full of love in their arms. It's not a character flaw, but it is important to be aware of the reality of adoption. It can be a beautiful choice, but not for everyone.
Older children who are put up for adoption often have been neglected and/or physically or sexually abused. Parents who adopt have be emotionally and educationally prepared. Parents sometimes have this Hollywood love portrait painted in their heads, thinking that they are going to rescue the child, and that they child will fall into their arms and love them. The research on the effects of neglect and abuse on children, especially foster children who have jumped from home to home can paint a depressing picture. These children need a lot of love and patience and is someone hasn't had the training, the time, or the social support, it can be a difficult journey.
Watch the documentary "Wo Ai Ni" (I love you, Mommy). In this, a Jewish-American couple adopt two Chinese girls. The older daughter who was brought over at age 8 (for the purpose of being company for their other daughter), cried for weeks. There was so much anger and sorrow in her sobs. She knew no English, missed her home in China and all her friends. Her parents were so frustrated with her. They wondered why she was so sad when she had it "so good" in America with lots of toys. It made me ache so much for the little girl. A house is not a home, especially when you are stripped way from everything you know and placed in a foreign land, expecting to show love to strangers. Her parents kept telling her that they loved her early on, but for a little lonely child who saw them as strangers, it doesn't mean much. About a year or so later, the girl caught up with her English, BUT since her parents made no attempt at trying to keep her connected with her heritage, she lost almost all of her Chinese. She used to Skype with a friend of her's (I think she was another adoptee) in China, but at the end of the documentary, she could no longer talk to her friend! She needed a translator. Often, families of internationally adopted children keep life books, keep them involved in their culture, etc. Adoption is often very complicated, and people who take that route need to be prepared. It's not as simple as, "let's just adopt a child".
Anyway, we don't just have children for the purpose of passing down genes. We're more advanced than that. We do it for a sense of love, closeness and a sense of "family" and connectedness. I think we're driven to have a sense of family, and having children is a part of that. The environmental reasons and other problems may be a concern, but it doesn't water down our inner need for a family.
I remember reading this when it first came out in 2010, and the sadness I first felt still lingers. The lying and covering up by the agencies about emotional problems and the horrible acts of US parents (murdering/abandoning their adopted children) breaks my heart. Most cases do not end this severely, but it doesn't take away the point that you must be informed/educated/prepared when you adopt (especially if they are not infants).