If they don't know enough about the world (or don't know enough about the physical structure of places or about people or about houses or about land use) they're more likely to design in patches. Give a character a house that sits on a lonely hilltop, for instance. Make the lonely hilltop bleak (for atmosphere) and brutal (no water, not much usable land) to give the character a solid environment. Then put a town in a fertile valley not a hundred years from this lonely hilltop. And, on the other side of the lonely hilltop, have an equally lonely road where no-one passes. It's a road, though, not an almost-invisible track, even though there is no government (despite the town, which is on a different road anyhow) and despite the fact that no-one passes. And then, suddenly there is an inn. With enough food at all times and with company (perhaps jolly, perhaps dangerous). Thinking about the scene in terms of a fantasy novel first and foremost, can lend to this patchiness.
This is because thinking first and foremost "I am writing a fantasy novel" can lead to world building from stereotype. "I need a fantasy world so it must have these characteristics." Given enough solid thought and the road can dwindle to a shack and the inn can disappear and the valley with its town can be further away and in a different micro-climate underpinned by quite different rock types*.
Some of this, however, is something else. It's building different aspects of the world on different pieces of paper without bothering to see if they fit. I evilly tested this on my students last Tuesday, and it was a lot of fun. For me it was a lot of fun, but not for the students. One group suffered questioning from me when their lowland house with its stream running underneath ended high on a granite hillside, for instance. This is a very good and thoughtful class, which made the source of the problems particularly obvious.
Until recently, I thought that the problem was with lack of knowledge about the basics of world building and the resort (through lack of knowledge) to fantasy tropes. That's the problem for some people.
For others, though, the problem derives from the simple mechanics of how they went about their early world building. If you start (as I made my students start) with your main character's home, then put the page aside and start designing the town, it takes a conscious effort to realise and define their relationship with each other.
And that's my thought for the day. I can now turn my brain off.
*And the solitary resident on the bleak hilltop can have a well, for life is not tenable without water. Though more than one writer-in-training in most classes is not sure of this.