This years ramadan is coming to its end...and traditionally people go back to their hometowns to visit their family.
As Jakarta is host to many from around the country, it results in a mass exodus. Many companies have a mass leave policy to allow their staff to return home. In some cases companies sponsor buses for their staff.
As a result flights, buses, trains are booked way in advance. Jakarta seems to go into hybernation mode for at least a week.