It isn't just low wage workers. I've seen obviously sick workers in all sorts of settings. When I was in labor with my son, an attending nurse had a nasty cold, looking run down and constantly wiping her nose, etc. So naturally my newborn son, who never left the house after leaving the hospital, got his first cold during his first week of life. I told my mother about it, as she was also a nurse in the same hospital, and she said that nurses aren't supposed to come in sick but sometimes do, always claiming that it's allergies.
I'm a teacher, and there was a coworker who worked for a whole week before Christmas with a vicious chest cough that you could easily hear down the hall. She worked directly with students, attended a hands-on team-building activity with the whole staff, etc. She's single & I suspect that she would have been lonely staying at home. Completely irresponsible on her part and I avoided her as much as possible, sanitizing constantly as we had a Christmas week cruise planned.
These kinds of jobs do include sick leave, but some workers just don't want to take it. I do think it's a cultural thing ("I go to work no matter what!"), and I hope that Covid changes that aspect of American work culture.