The use of passport is an example of an attempt to do identity proofing. In the practice of identity management there's a concept of "Identity Assurance Levels" where you have varying levels of validation of a person's identity. If you are interested in this, check out NIST Special Publication 800-63A.
AirBNB is trying to use the passport photo as a way to link you to a real-world identity, cheaply. They are in a sticky situation because their bonkers business model will suffer if customers need to go through intrusive processes. Simultaneously, they need to do something to avoid being held negligent when a fake AirBNB host/guest hurts someone. The problem is that it doesn't really provide assurance of anything other than possession of an image of a passport.
The problem is that it's spewing alot of information that if handled improperly is a high risk for fraudulent use. For example, knowing your citizenship, date, and place of birth makes it trivial to fraudulently obtain your birth certificate. That makes it pretty trivial to do something like obtain a fraudulent driver's license.
There are many ways to do this more effectively and at much lower risk to the customer. For example, you could verify ownership of a bank account with trivial deposits. Or you could mail the customer a token. Or require a notarized document. Or some combination. But the risk to AirBnb of a negative outcome is low, so they push a risk that you may not understand to you.