I've been to Senegal. My son lived there for a while. We have very dear friends from Senegal. Most Americans don't realize that people from places like Senegal can't just buy a ticket and hop on a plane to come visit. We tried many times to get a US visa for a friend and were denied (each application costs money).
This is not coming here to work or get health care - just a vacation. We just wanted a bright, energetic young man to visit us and go watch a Cal basketball game, visit Yosemite, etc. for a couple of weeks.
Never happened.