The position of your listing depends on a number of factors from price, comments, availability and popularity in and outside airbnb.
To regain that good ranking you could try sharing your listing on Fbook and Twitter for a start. Even if you've done it already, it needs to be done regularly to ensure popularity of your listing in the eyes of 'bnb algo.
Properties using instant booking are also prioritized.
All that @Denis19 says, and also, new listings get priority over older ones. I suspect that the listing order shown to a potential guest is also designed to ensure the request will be accepted. For example, if you never accept short-notice bookings, your listing may not be on the first page when a guest searches for a place within the next week.