You also have a much easier route to fixing issues, since there will be far less politics involved. Probably you will also have a deeper understanding of the code since you wrote it.

This is true, but I've found it far more common that a predecessor at the company I'm at wrote the code and isn't around to support it anymore. For simple components it's no biggie, but for non-trivial components it can take about the same time to debug as an external module, the benefit of the external module generally being better documentation, although thats not a given.

If you find the fix yourself you don't need to deal with politics if you don't want to. Submitting pull requests is optional after all.

If you don't submit a pull request and get your fix merged, essentially you have given up on the benefits of an open source library maintained by other people. You will have to maintain your fix. At that point, you might as well have written the thing yourself, especially for trivial stuff.