Why are so many Airbnbs backyard ADUs or converted guest suites?

I’ve been looking through Airbnb and vacation rentals in Half Moon Bay, El Granada and the Coastside and noticed how many smaller 1-bedroom/studio listings are guest suites, backyard guesthouses, in-law units, above-garage spaces, or require access around/behind the main house.
Is there a local zoning/housing reason this setup is so common around Half Moon Bay? And for people who have stayed in HMB, did you care whether your Airbnb was a detached/front-facing space versus a backyard unit, converted portion of a house, or above a garage?
Mostly curious because Airbnb’s “entire place” categories can make some very different physical setups look similar in search results.