It could be multiple reasons. It could be of the partners jockeying for power and trying (successfully) to assert their ideas over the group. Maybe the partners want to bring in more international business and therefore want more "reliable" fixed hours. The partners could even be planning a merger or a sell-off, and want you and your co-workers to be nice acquiescent resources to be used as pseudo-collateral.
Any of these could be reasons for wanting a more regular, controlled office environment.