Being open source is it's biggest drawback. Anybody can modify the source code and create their own OS. So everyone started to code their own operating systems and now we are stuck with more than 500 distributions instead of a single distro which really works.
Really? How can being open source be a drawback? No way. Being open source give enormous benefits for any project, one of them is precisely the chance of forking, as it gives options to create more variants, fix bugs in original projects, creating diverse developments and most important of all it gives freedom from
vendor lock-in. Being free software also gives more option to users to collaborate modifications, bug fixes, report security problems and increased chances of them being fixed.
Compare that to proprietary software (like Windows). If you don't like newer versions, so sorry, you can't do anything but stay in the older. If you find a bug you can only report it and pray that the developer cares to fix it, the same as for new feature request or even if newer versions remove working features. And if the developer decides to not further offer the program, the community can't do anything about it but to stay with the latest possible version and hope it works while searching for a replacement.
Of course, something like the explosive development as Linux had, such a number of different distros may scare newcomers into choosing one, making a somewhat uninformed decision. This is a particular case rarely seen in any free software project, and even though it keeping it free is still a great pro for Linux.