Very few people here have been here long enough to know that the doors didn't weren't always a thing. I had been on the Island for about nine months, or so, before the first one appeared. There used to be a building that housed all the doors, so Jake would just have to walk in, and see if any appeared. I just assumed he did this on a daily basis, because I never sensed anything, and I have senses you don't have. Even with magic. Jake may sense something while he was blue, but he often found the doors while he was human too, so I don't think that is the case. The doors appearances has always been erratic, sometimes we would get two and three doors at a time, and then go months without one.
Here they don't have a special place that they appear in, so the places they can be found in is just as erratic as their appearance. And the doors always look different.