The option to sit changes who can stay long enough to participate.

Participation has a physical cost that standing rooms quietly charge. Someone with arthritis, a heart condition, chronic pain or simply eighty years behind them can attend an event with no chairs for about ten minutes, which is not long enough to say anything or hear the important part. Whether people can stay is decided by furniture long before it is decided by interest.

Count the chairs at anything you organise, and put a few where the conversation is rather than around the edges. If you are attending, notice who is leaving early and why. A seat is one of the cheapest pieces of access there is.