Because the only inhabitants of this island are monks they are praying and singing religious songs a lot. They also visit church very often and you see some student moks walking over the island and studying the bible.
Don't think it's unfriendlyness or that you are not welcome on the island, when you speak to one of the munks and they only knot their heads friendly but do not say a word. They can be in a period in which they are not allowed to talk or even have done a vow to not talk at all. Other munks are actually very friendly and open for a conversation, in which they no doubt will mention their beloved God and the word of the bible.