What is the cause of the changes that the speaker mentions? [originaltext]Attent

Attention, please. Due to expansion project, please note the following changes. All domestic departures will board in the main terminal building, at gates A and B. All domestic arrivals will deplane outside and passengers will be bussed into the main terminal. International flights will depart and arrive at the annex terminal, gates C and D. To get to the annex terminal, take the airport subway, which boards near gate A. Expansion work will last approximately 10 weeks. Thanks for your patience.