What’s the difference between a child going to daycare and getting sick vs. going to pre-school/kindergarten and getting sick? Do their immune systems get stronger with time?

I hear so many people argue against daycare by saying that kids get sick all the time, they bring the illness home, and you have to miss work when they are sick.

Kids are eventually going to preschool or kindergarten. What’s the point of avoiding daycare if they are eventually going to be in the same situation with school? Is it just to delay the inevitable or do kids immune systems get stronger with time?