Davkat,
The OC could have the power to do this depending on what resolutions they have passed… But more importantly it makes sense as to the approach being taken regarding this pest control. With pest control, it is only as good as the weakest link.
If you do not treat the total building, those creepy crawleys living inside people’s apartments that are not treated will have a nice little safe haven to live and bread in, only to reinfest the rest of the building sooner rather than latter.
There could be a further purpose to this pest treatment, including doing a pest inspection of all of common property to ensure there are no unwanted pests chewing their way through the building… Not that there would be much to chew in a modern building