I think it comes down to development cost. A lot of suburbs are developed by a single housing developer, and they essentially have a "theme" with similar styles and just a few floor plans to choose from. So some suburbs end up looking very cookie cutter. They also do things like clear all the old trees out prior to developing the land, which is cheaper and easier, but can create a very desolate environment to live in.

There are plenty of suburbs that aren't this way though, especially older ones.