In simple terms, the drivers and causation are accurate listings with strong online reputation which in turn helps build a  high business ranking in search.

For a discovery searcher to  convert into direct searcher there is a need for the business to first have a strong listings that can attract the customer.  This usually is the first set of information a customer can interact with. This information needs to be accurate and understandable so customers can easily find you.

A  second major key factor that would come to play subsequently is  the business outlook what we term "reviews". 

A good reputation online is a key factor that drives discovery searchers to direct because customers tend to advocate and keep going to a trusted brand.

There are other factors to optimize to improve conversions like social presences, posting relevant content, etc but the starting block is the two I mentioned above.