This is neither good nor bad. Often we can't tell why they wanted the change. But sometimes people do spot bugs because they have the source and we try to fix them when we can, again, balancing the changes against possible breakage, and in priority with other features and fixes that people are waiting for, and factoring-in where we want to go with the software. But software is still software, it's still a difficult process to make great software. The Netscape source code was a mess when they released it, so the open source team started from scratch, which is not a tactic unique to open source, all programmers new to a project want to rewrite it.
New code is simple.
Code that's used by millions of people often is a convoluted impossible to understand mess. We all make compromises. Intel does not release their source code. It's even worse. Try to find the line between open source and commercial software on Windows and Macintosh, both of which have active open source development communities, and both support dynamic linking that allow runtime mixtures of different philosophies.