I often wondered what the "good citizens" got out of the deal for housing the pregnant girls. (I am a native Oklahoman, and aware of folks who survived the wonderful institution.)
I know for my great-grandmother she got a help with the daycare she ran. I imagine families also got help with childcare or housekeeping. I doubt that was the primary motivator for many of the families. While we justifiably recognize these practices as horrific today, at the time, the "good citizens of Shawnee" certainly believed they were helping these girls. Living in a home was almost certainly preferable to living at Girl's Town. They felt they were helping the girls get a fresh start.
I wouldn't put it past at least some people to have been making money from the situation. However, I don't have any evidence of that. Most likely the people involved, and perhaps even the mothers felt this was a better option then staying at Girl's Town and going through the pregnancy in a juvenile detention facility.