If you notice, most of the girls even have actual addresses posted - including flat #.
The reason you have so many "independents" is somewhat historical.
I lived in HK in the early 90s, and around that time some clever triad lawyer discovered a loop hole in the prostitution law that defined a brothel as "more than 1 woman in a location...".
The natural upshot was a proliferation of tiny (even by HK standards) little flats (often with the typical yellow sign == red light) staffed by one girl.
Another thing I notice on the site is that the prices in the central "touristy/Gwei" areas like Tsim Sha Tsui are $800-$1000, while a girl in Tseun Wan - way out in the New Territories almost at the Chinese border - goes for less than half that.