The other 8 fingers cover the 8 holes of the zurna. These may not apply to zurna types and zurna music that I am not familiar with. The shape of the instruments internal cavity is like a parabole and therefore optimized to send the voice straigh ahead. You will notice it very well if a zurna player turns your way. The biggest hinder to learning to play zurna is this need to exert intense air pressure all the time.
Many people can do that.
The hardest part is to let air from the new breath into your mouth cavity without and unwelcome surge or drop in the air pressure there. Circular breathing makes it worse because then the pressure lasts as long as the song, instead of as long as each breath. The next biggest hinder is availability of reeds. You must learn to make them yourself. Humidity and molds are the keywords there.