Why? I mean, sounds good if you are sick, but rather you stay home.

Lots of people, for lots of illnesses, are infectious without really having any symptoms.

Plus most people still go to work when sick. They will just dose up on whatever drugs they have to hide the symptoms and make them feel better, then go to work anyway. Even here in Europe where the government pays sick leave that happens.

And before this pandemic that was generally considered a virtuous habit. I wonder if that will change when this is all over

As we have observed in the Covid-19 pandemic, It could be the case that you were just only lightly sick but also contagious. Not to mention also a few things are difficult to pass, for example, University lectures (skipping one can make it difficult to follow the next) and again lecture halls are cramped so you can easily infect somebody.