When I first started working, it was common for employees to have a certain number of sick days and a certain number of vacation days. If you got sick, you took sick days; if you didn't get sick, you didn't take them. Obviously this was ripe for abuse, but it had the virtue of meaning that employees who got sick could go home and get better rather than infecting the whole office with their bug.
Nowadays, we have PTO (paid time off), which is a combination of sick days and vacation days. Typically, PTO is the same number of days that you used to get for vacation back in the day. So now, whenever you take a sick day, you are losing a vacation day. So duh, of course people come in when they are sick, or else work from home; if they didn't, they'd be burning vacation days. If you ever wonder why the burger-flipper behind the counter at McDonalds sneezed in your burger, this is also why. It still shocks me to see people in food service jobs sneezing, but that's the brave new world we live in.
I think most 20-something and 30-something workers in the U.S. never experienced "sick days." So maybe this all seems puzzling to you, but it's dead obvious to me: if you want employees to go home sick when they are sick, don't dock their vacation time.
Of course, I'm completely glossing over the fact that lots of employees are part-time and don't even *get* vacation time. We have really impoverished ourselves over the past thirty years, with the invention of "PTO," with the rise of part-time work as a way to avoid paying benefits, with the rise of lifetime minimum wage employment, and a variety of other innovations.