- Fear - If we make the source available, our competitors will steal it and use it against us!! Unless you're developing military software, this really shouldn't be an excuse
- Embarrassment - I drank 8 redbulls and wrote this code at 3 AM, you'd make fun of me!! Fun fact: the internet is held together with hot glue and duct tape. Even if you think your code is terrible, other people could still probably benefit from it
- 3rd Party Plugins - I can't release the source, I'm using a paid plugin! Even if your code relies on proprietary 3rd party plugins, you can still release the source for your code
- To Scam and Cheat - Volkswagen vehicles detected EPA tests and switched them into a "low emissions mode", once the test was over, the car's software would go back to polluting If the source code for these cars was made available to begin with, they could have never gotten away with cheating on emissions tests like this
Open source misconceptions
Some people believe that if something is open source, it means anybody can change the code, like editing a wikipedia page. Other people say if a product is open source it's impossible to enforce the brand.