If you need you can call or email them. Like any business with new products and services these are tested in small groups, tweaked and then canned or launched.
You need to register on Airbnb ‘marketplace’ if you want to hire or host through Airbnb, new cities are being released all the time. You can easily google the cities already available.
Additionally anyone can invite a friend they know or hire many of the professionals out there offering their services and manually add them to your listing as a cohost.
You can but if you want to get offers via the Airbnb marketplace then you must be a local host with good record, usually a super host as this is what people need- a nearby host to greet guests, be there to respond to issues etc as the owner and primary host is mostly remote or busy doing other paid work.