Does p5.js or processing have any commercial use? If so, what type of business do you generally use?
I think its likely that you could probably make a genuinely good commercial app with processing, however a lot of things hold back the development of a high caliber application on processing.
As you might have noticed the ide is not considered ideal for development purposes, and is designed to be used with small sketches. As the lines add up code management becomes unweildly to downright disastrous. Also there is a severe lack of frameworks when it comes to processing which means that deploying a piece of software in a commercial setting, which will often require management updates and debugging might not be ideal, as usually software is managed by a team of people who understand how to code in a particular language and who have spent time perfecting the pipeline and utilizing the frameworks.
I think processing is best kept for small projects, arduino, raspberry pi, etc, where a small team of people are involved, and where the code is usually quite concise.
May be wrong, just my 2 cents.