That can help, though the office isn’t the only transmission vector. Schools, grocery stores, restaurants, public transit, etc. are all major vectors. Families with early school-age children especially tend to get sick a lot, as young children learn and play in close proximity but don’t tend to follow good hygiene habits.

There’s also just the issue that in any environment with multiple people, it only takes one infected person to infect everyone else. Different people have different tolerances for illness as well as varying severity of symptoms. Someone with mild symptoms may come to work/school anyway and the whole room gets sick.