Can someone help me with exactly why residential areas in Nigeria are always so haphazard. Houses are never in a straight line. Roads are never in a straight line. There's never greenery, there are no trees etc.

The picture shows a middle class residential community in the US and very few, if any, middle class area in Nigeria matches this. Not yaba, or gbagada or Anthony. Not even Lekki phase1 in my view.

No doubt, our uses of fences gets in the way, but even asides that the straight lines and the symmetry of the estate in the picture is just makes for a good environment.

I have observed it too and did long ago. The houses tend to be arranged like trees in jungles. No adherence to planning and most times the planning barely exist or aren't well handled.
One man extends his small land into the road and the next land owner uses that extension to adjust his until they are left with chaos. This is asides a concrete fence that leaves the whole place looking like border. Only areas with huge houses that fences cannot effectively cover have manageable views. Then tree planting and flower planting culture are next to zero.