This is sometimes due to the fact that doors are not being used in the respective cultures (as, for instance, in Yanesha’) or, as Nida (p. 45f.) explains, other cultural differences:
“One cannot say to the Zanaki people along the winding shores of sprawling Lake Victoria, ‘Behold I stand at the door and knock’ (Revelation 3:20). This would mean that Christ was declaring Himself to be a thief, for in Zanaki land thieves generally make it a practice to knock on the door of a hut which they hope to burglarize; and if they hear any movement or noise inside, they dash off into the dark. An honest man will come to a house and call the name of the person inside, and in this way identify himself by his voice. Accordingly, in the Zanaki translation it is necessary to say, ‘Behold I stand at the door and call.’ This wording might be slightly strange to us, but the meaning is the same. In each case Christ is asking people to open the door. He is no thief and He will not force an entrance; He knocks — and in Zanaki “He calls.” If anything the Zanaki expression is a little more personal than our own.”
Sources: Nida 1952 (Zanaki); Duff Tripp, p. 310 (Yanesha’); Reiling / Swellengrebel (Tzeltal, Zarma).
See also complete verse (Rev. 3:20).