Office restrooms have a completely different use case - they're not trying to turn over occupancy as quickly and cheaply as possible. And none of the office restrooms I've been in have ever used bar soap. And I have input into my office building's selection - I get to complain to the office manager who can then complain to the building management. The result is, typically, some hypoallergenic liquid or foam that doesn't over-dry most people's skin, so they have little reason to bring their own.