An open source project is primarily composed of people writing some software out of passion with few hard deadlines. A team of 200 developers, some off shore, are developing in order to get paid for a client who likely has strict time and budget constraints. I'm not sure I could come up with many scenarios that I would expect to see a wider gap in code quality, even if the developers were the same level of skill.
Also it's easier to nope a bad decision for OSS. Office politics makes it way difficult.
For one thing, an open source project typically has a stable set of one or more core contributors, who really care about the project.
I would wager that open source projects are most likely some of the best run projects in the world.
I suggest that you (re)read Cathedral and the Bazaar if you really are curious about the difference between a project worked on by 200 odd developers in a company and an open source project.