They're a collector item. Why would anyone want 50 salt and pepper shakers or plates that can only hang on the wall? Same idea. Tears in the eyes can be viewed as sweet, can remind one of how vulnerable a baby is and help them feel protective. Just a couple of ideas.
Later As I was helping my grandson who had tears in his eyes because he doesn't like to read I had the thought that the tears bring out my tender feelings. I suspect people like the doll because of how it makes them feel tender and protective.
I think these dolls appeal to older women who don't have children. I know I was attracted to them until I had the real thing.