Agreed. I think it's better to say it takes time up front. But the upfront work may take a while.

I spent six months last year writing explanations for a standardized test. It was extraordinarily boring. But now I get $1000-$1500 per month in licensing fees.

I think there are lots of passive income opportunities for developers to make passive income in non-technical niches.

For instance, I've only been learning programming for a few months, but I have a Wordpress blog. I'm probably going to buy that plugin. Always wanted to track that, but didn't know how.