I've relatives who adopted.
It's no longer the case that it's newborn or young babies or even toddlers that are the children needing adopted.
Access to free contraception, free abortions, the lack of stigma around young parenting now means that there just aren't lots of teen mums giving up babies from unplanned pregnancies.
Most of the children are ones who were legally removed from the parents for neglect, abuse, who have all the associated problems caused by this like fas, other disabilities and conditions. Plus the understandable psychological consequences of a chaotic early childhood.
Plus even where there's been clear abuser/neglect there's a lot of red tape to remove a parents rights.
Then there's numerous reasons people may not be suitable to adopt - their own health and psychological issues, finances etc or who just aren't temperamentally suited to coping with all the complex needs of adopting a child who's had a difficult start.
Plus not everyone wants to even consider it - it's a very personal decision.
Prior to having dd I had 2 mc and a Dx that meant I may have not had my own child. I broached the idea with ex he wasn't interested. He'd no experience of it personally but had known someone adopted (school friend) and seen how it was a challenging decision to make and not one he felt able for. Whereas I had a different experience and felt positively about adoption.
We were able to have dd, but medically I couldn't have any more. But those medical reasons also ruled me out for adoption.
I do think it should become better known that single adults can adopt, I still come across a lot of people that don't know that.