Here are 2 things I could be wrong about:
-I believe there was a balcony/patio filter option many years ago and airbnb did away with it. I think I even used to use it back then. Definitely could be a memory I have just invented because I have been so frustrated that there isn't one.
-Either way, I think the reason that there isn't one could have to do with cig smokers? I have noticed that sometimes professional hosting operations (like the management companies that have multiple units listed), when they are listing flats with balconies, do not always necessarily advertise them, occasionally even (seemingly) downplay them in the photos. I always wondered if it may be to keep from flagging to smokers, of whom there might be 100 who would be using a balcony filter for every 1 using it just because they like the outdoor space. Only a theory.