The reluctance or in some cases refusal of workers to return to offices has shaken the real estate market. : Four years after Covid-19 filled hospital emergency rooms, closed schools and emptied out cities, US offices remain about half vacant. Office occupancy in 10 of the largest US metropolitan areas rose to a new high of 53% for the week ended Jan. 31, according to Kastle Systems, a firm that provides security to buildings. The firm’s barometer on how corporate return-to-office policies is going has been hovering around that level for 13 months.