You are probably one of the unlucky new hosts who are part of the pilot where you cannot turn off instant booking.
Clearly this has issues and risks for hosts - you have no opportunity to have any discussion with potential guests to see if they are a good fit for your home. It's particularly so where guests are sharing the space with you - as opposed to a stand alone unit.
From and AirBnB perspective it's a good revenue generator as it allows and encourages impulse buys by guests.
There has been a lot of negative feedback from new hosts and existing hosts too - so you should provide your feedback asap on this issue.
Some new hosts have reported that if they close their account and open a new one, they are able to disconnect instant booking as it seems like it is a % of new hosts that are being enrolled without their knowledge in the pilot.